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Tailings Pond #1 <br /> File No. M-77-378 <br /> Page 2 <br /> III . Overburden Covering, Cont 'd <br /> Areas that are anticipated to curry additional runoff volume <br /> over that from uniform sheet flow will be underlain with <br /> additional compacted overburden material. Specific examples <br /> would be at the base of any benches, if required, and the <br /> pond-hillside interface . The most concentrated flow will be <br /> at the pond-hillside intersection which at the west end will <br /> carry the total surface runoff from the 9 . 5 acre pond top. <br /> This flow is estimated to be 40 cfs with a 1001-year <br /> thunderstorm event (2 . 3 inches in 1 hour) . In order to <br /> reinforce for this flow, an area ranging in width from 10 feet <br /> at the east end (small contributing area) to 20 feet at the <br /> west end will be subexcavated 3 feet with 2 1/2 : 1 side-slopes . <br /> The bottom 1 foot will be replaced with one foot of overburden <br /> material compacted to 95% of its maximum dry density. An <br /> additional 1 foot of loose overburden material will be placed <br /> on top and the area seeded . If necessary, erosion control <br /> fabric will be placed to minimize erosion. This area will not <br /> slope transversely and the 1 foot depth should carry the flow <br /> without backing onto the unr_einforced pond area (See attached <br /> calculation sheets) . The compacted overburden with a <br /> permeability in the range of 10 'fA to 10-"Icm/sec will control <br /> downward migration of the runoff water . <br /> Upland runoff will be controlled by the existing runoff ditch . <br /> Attached is a F.M. Fox generated hydrograph for this <br /> interception ditch as originally designed . <br /> IV. Seeding and Covering: <br /> The regraded area (approximately 27 acres) will be fertilized <br /> and seeded either in the fall after completion of earthwork or <br /> the following summer during late June or early July (depending <br /> on construction progress) . 'Phe s-e-cl mixture will be the <br /> "Mountain Mix" specified in Table E-4 of the Consolidated <br /> Permit Application. The seed mixture will be applied at 20 <br /> lb/acre (minimum) by hydroseeding. Prior to seeding the <br /> overburden will be analyzed to determine the type and <br /> application rate of fertilizer required along with any other <br /> amendments such as limestone. The borrow material is expected <br /> to be similar to that used on Tailings Pond #4 . The <br /> recommended treatment was application of 0 . 9 tons of limestone <br /> per acre and fertilization with 200# N , 40# P205 and 60# K20 <br /> per acre. A spring tooth harrow will be used to provide a <br /> thin soil covering after seeding. Secondary plant communities <br /> (forbs and shrubs) as committed to in the Consolidated Permit <br /> Application will be planted after establishment of the pioneer <br /> communities. <br />