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EXHIBIT 7, ITEM 23, PART H <br />Perimeter Area Sediment Control <br />Situations similar to that described in Part G are anticipated elsewhere in the operation for which <br />specific areas and activities cannot be identified at this time. Some activities are contemplated <br />for limited disturbance outside the pit, spoil pile and mine facilities disturbance limits, but still <br />within the Disturbance Limit. These may include things such as power lines, transformer <br />substations, communication towers, mine development exploratory drill holes, ancillary roads, <br />dewatering wells and associated infrastructure, pipelines, etc. To accommodate such activities, <br />the Disturbance Limit has been moved a few hundred feet outside the actual pit and spoil pile <br />disturbance limits. This is depicted on Map 41 B, "Watershed Boundaries for Hydrologic <br />Modeling, Collom Area" (Volume 22). It shows as a roughly 300 -foot wide band just inside the <br />topographic tie-in boundary. For the most part, this shaded area will not be disturbed at all, but <br />the exact locations, timing, and specific dimensions of small area disturbances associated with <br />the above described types of activities cannot be fully identified at this time. <br />When and if specific areas within this Perimeter Area Sediment Control Techniques (see shaded <br />area Map 41B) are needed, and if they will have sufficient impact on the mine and reclamation <br />plan, they may have to be addressed via a permit revision. The base case if practicable will be to <br />simply capture the runoff via a contour ditch and re-route it through the existing sediment control <br />system or to the active pit utilizing small ditches. Ditch designs capable of handling up to 100 <br />acres of such disturbance are presented in this Part H. For example, a 3 -foot deep triangular <br />ditch with 3H:1V side slopes and a bottom slope of 4% can convey the 10 year, 24 hour runoff <br />of 18 cfs from a 25 acre site at acceptable velocity. Similarly, trapezoidal ditch with a 8 foot <br />bottom and 3H:1 V side slopes and a 4% bottom slope can handle the 29 cfs runoff from a 40 <br />acre disturbance with acceptable velocity. <br />Finally, for areas which cannot practicably be captured and re-routed, the sediment control <br />provisions of CDRMS Rules 4.05.2 (3) and 4.05.5 (2) will be used. <br />More specifically, the practices described in CDRMS Rule 4.05.5 (2) (f), which are "near <br />source" practices include but are not limited to: <br />• straw dikes/bales <br />• rip -rap <br />• check dams <br />• mulches <br />• vegetative sediment filters (a.k.a. "grass filters") , and <br />• small dugout ponds <br />The selection of which of these are most practicable at a given small ancillary disturbance will <br />depend on the size of the small disturbed area and the local topography. One practice is <br />discussed in more detail below to demonstrate that the runoff from any of these areas can be <br />shown to meet the effluent standard (0.5 ml/l settleable solids) simply by flowing over <br />immediately downstream existing native vegetation viewed as a "grass filter". Cases evaluated <br />show that runoff from a 100 by 100 foot pad should meet the standard after having passed <br />Exh. 7-23H-1 Revision Date: 11/09/15 <br />Revision No.: PR -04 <br />