2013-05-20_REVISION - M1984094 (7)

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Section 7.0. Sediment Control System for Operation The permit area is basically divided into 2 areas, the eastern area that contains significant pre -law dis- turbance and the western area, which has only begun to be excavated. The eastern area primarily drains to the Plant Settling Pond and the Plant Infiltration Pond. There are other numerous piles and valleys which trap runoff and infiltrate it into the ground. Due to the extremely porous nature of the gravel, the numerous depressions and the 2 main ponds present in this area, there has never been a problem with disturbed area runoff leaving the site. All runoff from this area is trapped in the depres- sions. For this reason, no new sediment control facilities are planned for this area. There are some minor areas of pre -mine hydraulic mine disturbance outside the depression area that do drain off site but they have nothing to do with the current operation and are not collected by the ditches or the de- pression area. Also, these areas consist of large cobbly material that does not cause any issues with off site sediment delivery. All of the disturbance related to this mine either drains to the sediment pond or the depression area, as shown on Map C -2. For the western portion of the permit, a system of two collection ditches and one mine sediment pond will be installed to trap runoff and provide 24 hour detention time. As shown on Map C -2, Collection Ditch #1 will be along the northwest perimeter of the disturbance and will parallel Sacramento Creek and then turn east to the Sediment Pond. Collection Ditch #2 will deliver disturbed area runoff from the north portion of the permit area. The ditches will be constructed of the existing site gravel, which is very porous and it is likely that runoff water will never even reach the pond, since it will infiltrate into the ground rapidly, as it does in other areas of the permit. The pond will be constructed to contain the 100 year event from the disturbed drainage area, thus eliminating the need for a discharge permit. The pond will also be entirely incised and its bottom will be the same porous gravel that allows significant infiltration. Map C -2 shows a maximum drainage area that will enter the pond of 33.40 acres. A CN of 60 is assigned to the gravel since it is nearly void of fines and almost all runoff penetrates into the ground very rapidly. Once the mining pit moves into the area, all runoff will enter the pit, but the sediment system of the pond and the two ditches will be left in place until the site is reclaimed. The calculations to demonstrate that this pond is adequate to contain the 100 year 24 hour event are shown below: Gloria Z Mine 2013 Amendment 19