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RULE 4 PERFORMANCE STANDARDS <br />seasonal runoff events. Contour furrows will be created with regular frequency on slopes greater <br />than 20% and less frequently on areas between 10% and 20% slopes depending on the length of <br />the slope and the size of individual reclamation blocks as determined by topsoil laydown <br />progression in any given year or series of years. Past reclamation efforts undertaken in the East Pit <br />provide a general context to the likely construction frequency of contour furrows in the West Pit <br />and Section 16 reclamation areas. The steeper slopes in the South Taylor area will likely require <br />the construction of contour furrows at a greater frequency than previously mined areas. As <br />indicated under "Mulching Techniques" in Section 2.05.4, use of mulch would be considered a <br />last resort, but is certainly an erosion control metric that may be utilized (where deemed necessary) <br />for long south -facing slopes such as in South Taylor. Spoil will be graded to minimize long, <br />uninterrupted slopes. Replacement of topsoil will be followed by chisel plowing and contour <br />furrowing (when necessary). <br />The use of these soil stabilizing practices on areas currently undergoing reclamation at Colowyo <br />has been very effective in controlling surface runoff, thereby preventing surface erosion and <br />gullies. The efficacy of these mechanical techniques will continue to be closely monitored as <br />changes to the reclamation program are initiated. <br />4.15.5 Grazing <br />All the lands reclaimed by Colowyo will not be grazed by livestock for a period of at least three <br />years after seeding or planting and will be managed to promote the postmining land use. <br />Grazing by livestock will not commence until Colowyo has demonstrated to the satisfaction of the <br />Division that the vegetation on the reclaimed surface is adequately established and can be expected <br />to withstand grazing pressures. Any grazing studies undertaken by Colowyo will not preclude or <br />interfere with postmining vegetation sampling as required in section 4.15.8. <br />4.15.6 Field Trials <br />In 1975 Colowyo funded a revegetation study that was initiated on the Colowyo property by the <br />Department of Agronomy at the Colorado State University and the Colorado State University <br />Experiment Station. The study was designed and the work was monitored mostly to determine the <br />suitability of using native species at the mine site. Test plots were used to simulate the disturbance <br />that would result from surface mining. <br />The complete details of the four-year revegetation study are found in Exhibit 10, Vegetation <br />Information. <br />Also, in 1977 an additional shrub study was initiated in conjunction with the Soil Conservation <br />Service, Upper Colorado Environmental Plant Center. Approximately 35 species of shrub <br />seedlings from the Plant Materials Center were being evaluated for potential use in mined land <br />revegetation. <br />Field trials have been, and continue to be, an ongoing effort at Colowyo since these initial studies <br />indicated above (1975 and 1977). The most recent evaluation of efforts to establish shrubs and <br />Rule 4 Performance Standards 4-49 Revision Date: 5/25/18 <br />Revision No.: RN -07 <br />