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WL-PM-E/Letter to: DRMS Subject: Response to Comments <br />• 5. Geotechnical Stability. <br />Stability of all slopes on BLM land must meet the BLM's "mitigation measures" as stated <br />on page 1 and 2 of this letter. BLM requirements, including specific location of many <br />storm water controls and other features, will be more specifically stated during quarterly <br />inspections by that agency. The applicant/operator proposes conditional approval by <br />the Division pending continuing further confirmation of the stability of the material (both <br />exposed surfaces and backfilled slopes) as extraction continues. <br />a. As requested, this explains the methods used, including applications and materials, <br />based on the specified areas (as defined by slope and materials) which must be <br />stabilized: <br />1. Roadways: Roadways are generally a grade of l OH:1 V, and will be stabilized by <br />construction of compacted subgrade and base-course, followed by gravel (in <br />turn stabilized by compaction and use of mag-water or other dust control <br />agents) or paving. <br />Road side-slopes and side-ditches, where present, will have similar longitudinal <br />grades (1 OH:I V) and normally side slopes of 2H:1 V or flatter. The objective will be <br />to have 3H:1 V slopes on the shoulders of the road and wherever possible. All <br />slopes will be constructed by placement and compaction of fill, placement of <br />soil, and revegetation with grass. Ditches will be stabilized by placement of <br />• water bars, rock check dams, and armoring with cobbles, as well as temporary <br />placement of erosion control logs, straw-bales, and silt-fencing where needed. <br />If steeper slopes (ditches or side-slopes) are necessary, the slopes will be <br />stabilized by several methods based on the condition of the exposed or <br />backfilled slope and space available: <br />a. Benching, height not to exceed six feet, with bench tops having soil and <br />planting of grass. <br />b. Placement of selected large rock (boulders and cobbles) on the face of <br />slopes, together with selected placement of soil and planting of grass and <br />shrubs, as retaining walls, not to exceed six feet in height. <br />c. Use of geogrid on the face of slopes and between lifts of compacted <br />backfill. <br />2. Backfilled areas will be graded to 2H:1 V (3H:1 V whenever possible), and <br />compacted as placed, then graded with rills perpendicular to the slope, have <br />topsoil placed and graded (again with rills perpendicular to the slope), and <br />revegetated with grass and other plants as required by BLM. In addition, as <br />required by BLM (see page 1 and 2), rocks, trees and shrubs, and woody debris <br />will be placed on visible slopes to aid stability and provide for a more pleasing <br />appearance. <br />3. Cut slopes where bare bedrock (shale and sandstone - cemented materials) is <br />• exposed will be graded to 1:1 whenever possible, but will not have soil placed <br />on them; the individual slope areas will be evaluated on a.case-by-case basis for <br />PROJECT: Montoya Pit M-1980-146 AM-4 15 July 2010, Page 4