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• head of 1.0-foot above the riser crest was allowed during passage of the design peak flow. The peak flow used for initial design was the unrouted inflow determined by methods described in TP-149. This inflow rate was compared with the peak inflow rate generated by the WASH subroutine of the DEPOSITS model to determine if any adjustment in spillway sizing was necessary. In all cases, the larger of the routed flow hydrograph generate by WASH or the peak flow generated using TP-149 was used for final primary spillway sizing, resulting in a somewhat conservative size estimate for the spillway. Final primary spillway sizing took into account orifice flow into the riser perforation, orifice and wier flow into the riser, and pipe flow through the spillway conduit. All risers are fitted with a splitter-type antivortex device and trash rack at the entrance, as suggested by Chapter 6 of the NRCS Field Engineering Manual. Specific details can be found on the pond drawings shown on Maps 34, 78, 79, 80 and 80A. All emergency spillways were designed to safely pass the unrouted peak inflow rate resulting from the 25-year, 24-hour rainfall event. The emergency spillway on pond DP-1 was also sized to pass the unrouted peak inflow rate resulting from the 100-year, 24-hour storm. Spillway dimensions were based on criteria set forth in Section 4.05.3 and in NRCS Technical Release TR-35 CUD Method of Reservoir Flood Routing}. All spillways are constructed in non-fill earth material and are appropriately tined with riprap to allow a maximum outflow velocity of 12 feet per second during passage of the design peak flow, thereby reducing erosional hazards. The foundation materials for all the ponds are classified as silty clay loams and characterized (by the NRCS) as having low strengths and being prone to erosion and piping. Natural material subject to seepage forces, such as the downstream side of semi-in situ ponds, is protected from piping by toe drains or liners if required. In addition, anti-seep collars are provided along the primary spillway conduits extending through the dam embankments. These collars have been designed using methods contained in the EPA publication EPA-625.3-76-006, "Erosion and Sediment Control". Soil surrounding all spillway conduits is carefully compacted to further reduce seepage through the embankments. All pond embankments are constructed of clean cohesive fill material which has a liquid limit between 30 and 50, a plasticity index between 10 and 25, and containing at least 70% passing the U.S. No. 200 sieve. Toe drains are constructed of free draining granular material meeting the requirements of ASTM C-33 Concrete sand. The "D" Portal Area sedimentation pond DP-1 has a toe drain. The entire pond is lined with a one foot thick layer of cohesive material meeting the same requirements as the embankment material. • The liner and the face of the dam is covered with a 6 inch layer of compacted gravel which protects the liner during sediment cleanout operations. (Permit Renewal r`e3, 8199) v-13