2019-02-08_PERMIT FILE - C1981019A

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RULE 4 PERFORMANCE STANDARDS followed depending on the resulting community that evolves (see Section 4.15.7 above). For grassland testing the weighted average approach (Rule 4.15.7 (4) (b)) will be utilized where reference area data and revegetated area data are "weighted" (each combined into single values for comparison) based on the proportional acreage of pre -mine communities within the disturbance area footprint. Testing will then follow procedures detailed under Rule 4.15.11 (2) with preference being given first to subsection (a) [direct comparison], second to subsection (c) [reverse -null testing], and third subsection (b) [classic t-test]. For "targeted" Post -2008 sagebrush steppe revegetation (targeting the rangeland land use subcomponent of wildlife habitat), herbaceous cover will be considered adequate for final bond release if it is not less than 70%* of the sagebrush reference area's herbaceous cover with a 90% statistical confidence utilizing a standard students statistical t-test comparison of the means. If necessary, a reverse -null hypothesis testing procedure may be utilized in accordance with procedures detailed in Rule 4.15.11 (2) (c). As allowed under Rule 4.15.8 (3) (ii), relaxation of the herbaceous cover standard for areas targeting wildlife habitat post -mining land uses is designed to compensate for revegetation techniques (prescribed ecological reclamation approach) that must discourage grasses to encourage shrubs in the post-revegetated community. For "evolved" post - 2008 sagebrush steppe revegetation, the grazingland cover standard will be maintained. A higher percentage of herbaceous cover is not practical or desirable for the following reasons: It is well documented that in mined -land reclamation the establishment of shrubs to reach bond release levels has proven to be very difficult. Perhaps the most detrimental condition affecting shrub establishment is the competition from herbaceous vegetation. At a minimum herbaceous cover, levels should be less than the premining condition. If the herbaceous levels to be obtained were set higher than the premining condition, the ability to achieve bond release levels for shrubs would be most adversely affected. Higher levels of herbaceous cover would adversely compete against woody vegetation and hinder its successful establishment. 2. In mined -land reclamation, it is important to have adequate herbaceous cover to provide for erosion control. The reference areas at Colowyo indicate herbaceous cover values of 41.8% and 30.17% for the mountain shrub and sage reference areas, respectively. Colowyo is located at approximately- 7,300 feet in elevation. The period of highest potential erosion occurs in the springtime during snowmelt. At this time of year, erosion control is provided almost exclusively by herbaceous vegetation. Erosion control by shrub cover is virtually insignificant since the potential erosion occurs from snowmelt rather than raindrop impact. Therefore, if pre -mining levels of herbaceous vegetative cover can be re- established, logically a comparable level of erosion control will be achieved. The value of 70% has been selected given the following rationale. 1) herbaceous competition must be significantly restricted to facilitate emergence and growth of shrubs as indicated under Rule 4.15.11 (3) (ii); 2) the original value is 90%; 3) a value of 50% seems too low to adequately control erosion; 4) by regulation (4.15.11 (3)(a)) a reduction to 70% is allowed for one of the demonstrations for revegetation success for woody plant density; and 5) 70% of the herbaceous material in a native reference area should be adequate to control erosion on slopes 10% or less. Rule 4 Performance Standards 4-64 Revision Date: 11/27/18 Revision No.: TR -129