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RULE 4 PERFORMANCE STANDARDS <br />Topsoil Stockpile/Pond Embankment Seed Mix* <br />Western wheatgrass @ 4 Lbs PLS /Acre <br />Thickspike wheatgrass ** @ 4 Lbs PLS /Acre <br />Yarrow * ** @ 0.15 Lbs Pls /Acre <br />*mix will be modified as a result of an updated Reclamation Plan submitted after PR -02 approval. <br />Colowyo existing permit Section 4.06.3 must be modified to reference the updated seed mix in this location at that <br />time. <br />* *option to replace Thickspike wheatgrass with Beardless bluebunch wheatgrass or Sheep fescue <br />** *option to replace Yarrow with Cicer milkvetch <br />4.05.7 Discharge Structures <br />The sedimentation ponds at Colowyo are designed to treat the theoretical 1Oyear, 24 -hour storm event in <br />accordance with Rule 4.05.6(3)(a). As such, the general operation of the ponds will be a passive discharge <br />system where water is allowed to discharge automatically as necessary. Colowyo will sample discharges as <br />appropriate to remain in compliance with applicable CDPS Permit requirements. Pond dewatering through a <br />manual headgate may be performed as necessary to lower the water level depending on operational <br />requirements. Manual dewatering of ponds will meet applicable CDPS Permit standards. Discharge from <br />sedimentation ponds will be controlled by energy dissipaters and flow check devices where necessary. All <br />ponds utilize separate principal and emergency spillways with the emergency spillway located at a minimum <br />of 1 foot above the elevation of the maximum water surface during the discharge of the 10 -year 24 -hour storm <br />event through the principal spillway. The principal spillways are designed for the 10 -year, 24 -hour storm <br />event and the emergency spillways are designed to pass the 25 -year, 24 -hour storm event in accordance with <br />Rule 4.05.6(5). The design requirements can be found on each of the pond as -built drawings or in Exhibit 7, <br />Item 15 of the existing permit document. All sedimentation ponds will provide a non - clogging dewatering <br />device or conduit spillway to remove water storage from inflow. <br />4.05.8 Acid - forming and Toxic- Forming Spoil <br />Acid forming materials do not exist within the overburden to be removed by the mining operations. A <br />discussion on the overburden at the Colowyo operation has been conducted as set forth in Section 2.04.6. A <br />discussion of the overburden monitoring plan is set forth in Section 2.05. Acid -Base Accounting shows that <br />almost none of the encountered interburden has a net acid - generating potential, and the average acid - <br />neutralizing potential to acid - generating potential ratio ranges from about 50 to about 90 in each borehole in <br />the proposed pit, indicating that there is 50 to 90 times more acid - neutralizing potential than there is acid - <br />generating potential in the interburden (Exhibit 6, Item 6). <br />4.05.9 Post - Mining Impoundments <br />Colowyo constructs small impoundments on reclaimed areas in accordance with Section 4.05.9 of the <br />CMLRD regulations for Coal Mining, 3/21/01. These small impoundments are essential and basic to the <br />management of the rangeland post- mining land use of livestock grazing and wildlife habitat. The design of <br />post- mining impoundments provides for structures having a vertical height less than five feet from the bottom <br />of the channel to the bottom of the spillway and impound less than two acre -feet of water. As such they are <br />exempt from Division of Water Resources, Office of State Engineer requirements. Water harvesting ditches <br />may also be used to enhance the function of the impoundments, which is consistent with practices employed <br />on adjacent rangelands. <br />South Taylor /Lower Wilson — Rule 4, Page 8 Revision Date: 10/31/13 <br />Revision No.: MR -129 <br />