2010-04-27_PERMIT FILE - C1981012A

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• contain 10-yeaz 24-hour storm event runoff from pond 006 and 007 drainage areas, a total of 6.6 acre-fl. In addition, the Universal Soil Loss Equation was used to estimate sediment yield from these areas at 0.3 acre-ft/yr (0.9 acre-R for 3 years) at a conservative 1.0 sediment delivery ratio. The total required capacity for Pond 007 is therefore 7.5 acre-R. As shown by the stage volume curve for Pond 007, 9.2 acre-fl of storage is available in Pond 007, allowing a surplus of 1.7 acre-ft. The emergency spillway is adequate for passing peak 25-year 24-hour flows from both drainage areas while maintaining 1 foot freeboard. Exhibit 19, Section 1 contains SedCad documentations that indicate Ponds 005 and Pond 007 can be operated with the gate valves open and that sediment effluent limitations can be met. However, precipitation events sampled in 2003 indicate that under current conditions, effluent limits at Pond 007 may be exceeded. Thus PPLLC will operate this pond with the gates normally closed, until such time as it can be demonstrated, either by maintenance or reclamation practices, that effluent limitations will be met. All sampling during discharge events will be conducted in accordance with the approved NPDES permit to determine actual compliance with limitations The SedCad analysis for Ponds 005 and 007 was an analysis of an installed perforated riser at each pond under existing subwatershed conditions that had been previously analyzed in the permit. The data used in this analysis, including watershed area calculations, was taken from calculations performed for the design specifications of Pond 5 and 7 in Exhibit 19 of the permit. The drainage areas map in Exhibit 19 shows the watershed drainage areas for ponds 5 and 7. Drainage area 005-I is the total drainage area for pond 005. Drainage areas 006-1 through 006-5 and 007-1 through 007-6 all • constitute the total drainage azea for Pond 007. PPLLC will also open the gates on all other sites. A staff gage will be installed on or adjacent to the riser pipe of Pond 007 identifying the water level (7373.3 feet) adequate to retain a 10-year 24-sour storm without discharging over the emergency spillway. Tlris elevation was arrived at through a review of the Pond 007 as-built stage volume curve dated 5/31/85 in Exhibit 19. The crest invert emergency spillway volume is 9.2 acre feet and the 10-yr 24-hr runoff volume is 6.6 acre feet, resulting in an allowable permanent storage and sediment volume of 2.6 acre feet. PPLLC has received approval from CDPI-I&E, Water Quality Control Division to use a flocculent to settle suspended solids in pond water during emergency discharge situations or for water discharges associated with pond cleaning activities. All materials removed through the cleaning or excavation of sediment and/or treatment ponds will be disposed of at the development waste pile according to approved Minor Revision 24. • RN-004 2.05-10a (Revised 5/24/04)