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adversely affected, the Impacts oT the sediment ponds on tlormstream users will be mi nimaT. <br />Effects of Sediment Pond Di scharges, Dtveraions~ and Cul warts at Roed Crossings an Surfata <br />Nater puali tv. The effects of aedtment~pond discharges on stream water quality will be <br />negligible. All sediment ponds ere designed to ~contatn the 70-year, 24 -hour runoff <br />volume plus sediment. Based on several years of NPDES noni cots ng at the Nucla Mine, pond <br />tliachargsa should be lima tad to the 001, DD6," a~ probably the proposed 007 pond. A <br />mods ti cati on to the existing NPDES permit for the Nuela Mine will De applied for which <br />will incorporate the proposed 007 pond. To date, no di schargas have been observed at the <br />outfalls of Pontls 002, 003, 004 and 005. <br />Tables 77-24, 17-25, and 17-26 present mean annual values of select chemical parameters <br />representative of both the irrigation (mid-April through mid-Ottobar) and non-irrigation <br />seasons at NPOES Sites 007, 006 and Site SN-iii,. reapeeti valy. During both seasons, TDS <br />concentrations have remained fairly consi etsnt over time at both NPDES 001 and 006. Also, <br />levels of total Iron. di saolved iron and total manganese have never exceeded the effluent <br />criteria outlined in the exiatinq NPDE6 Permit (Na. CO-0000213, see Appendix 7-6, Tab 7). <br />• Dvri ng the li Fa of mS ntng operations at both the Nucla Mine and Nucla East mining area, <br />dl versions and culverts will be employed to control surface runoff within and arou~ the <br />disturbed erase. Five temporary di veraf one will be constructed in both areas to prevent <br />addlti onal surface water runoff from entering di sturDed areas and to convey runoff to <br />sediment ponds (see Tab 13, Facf 7iti eel. <br />All di veraiana are designed to handle the runoff free a 70-year, 24-twat runoff event. <br />Peak dt saharge rates for each diversion were determi mad using SED IIt07 II . Calculated <br />channel veloeiti es were found to be well under design-limit velocities. <br />Culverts have also been designed to pass the 10-year, 24-hour, and in soma csaea, the <br />25-year, 24-hour runoff avenE us imp SEDINOT I1. Culvert headwater design incorporates <br />adequate freebosrd of a minimum of one foot. Cul wart outlets on appl icabin sediment ponds <br />will be rfprapped to reduce the potantSal far erosion baton the outfalla. In addition, <br />periodfc inapxti ens will ba conducted at the other culvert sites to insure that any <br />accelerated erosion at the culvert outfa7lc does not go unchecked. <br />1 The effects of sediment porW diversions and culverts on surface water quality will De <br />17-78 Ravi sad 04/11/88 <br />• REVISED MARCH 2006 Attachment 2.05.6(3)-2-89 <br />