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WEIGHT) AND STRENGTH PARAMETERS OF COHESION AND ANGLE OF INTERNAL <br />FRICTION OF COAL PROCESSING WASTE MATERIALS WHEN THE FIRST BENCH OF <br />THE GOB PILE REACHES HALF TO THREE/FOURTHS THE DESIGN HEIGHT, AND <br />DEMONSTRATE TO THE DNISION THAT THE PROPOSED FILL, AS APPROVED, WILL <br />BE STABLE WITH A MINIMUM FACTOR OF SAFETY OF 1.5 <br />3. The proposed [Rules 4.09.1(3) and 4.10.3(5)] lateral subdrain system is innovative and should <br />substantially contribute to the stability of the proposed coal mine waste bank. It provides for <br />withdrawal of [eachate and moisture from the coal processing waste in the bank, and intercepts <br />moisture that may migrate along the bank-subgrade interface. However, due to the location of the <br />proposed waste disposal area, steepness ofs[opes, natural drainages, and geologic and ground <br />water conditions as described in the application, the Division considers it advisable to supplement <br />the proposed subdrain system with the subdrain system descriptions of Rule 4.09.2(2) in Gulch D <br />and the drainage to the west. Groundwater in undisturbed subgrade will likely still,/low <br />perpendicular to original ground contours, and, along with subsurface flows in the ravine bottom <br />materials from regions above the bank, manifest themselves to the thalweg of natural drainages. <br />The vertical reliefdrain would draw any such groundwater directly from the area. The lateral <br />drains should not 6e in hydraulic communication with the vertical drains, as they might <br />inadvertently permit the infiltration [Rule 4.09.1(13)) of water collected near the thalweg of the <br />ravine throughout the footprint of the bank. Please mods your design to incorporate, in addition <br />to the proposed lateral subdrains system, an isolated subdrain system as described in Rule 4.09.2. <br />Such vertical drains should be installed in both Gulch D and the ravine immediately to the west. <br />The Division concurs with BRL's response. Vertical drains have been added (Figure 2, Volume <br />IX). The applicant presents an adequate and thorough demonstration that an altemate subdrainage <br />system (size) ensures the applicable static safety factor, stability of the fill and protection of the <br />surface and groundwater (pages 5 and 6, Volume I7{, and Figure 2). The Division approves the <br />alternate design [Rule 4.10.3(5)]. Revised pages 1 through 13, the Table of Contents and Figure 2, <br />all for Volume IJ{, were included in the submittal dated February 11, 2004. <br />4. Please indicate, on cross-section A-A' on Figure 1, the prepared benches and keyways and lateral <br />drains of the Lambert and Associates design. In difference to the location of the A-A' cross- <br />section, anote should indicate that the lateral drains terminate short of, and do not make <br />hydraulic communication with, the vertical drains. <br />The response is accepted. BRL revised Figure 1 and Figure 2 of Volume Df in the submittal dated <br />February 11, 2004. <br />5. Please add construction inspections of underdrainage systems to your list of items on proposed <br />page 9, Volume IX <br />The response is accepted. Page 10 of Volume IX was revised accordingly in the submittal dated <br />February 11, 2004. <br />6. Please indicate in your proposed inspections the use of color photographs in compliance with <br />Rule 4.09.1(11)(c). <br />The response is accepted. In the submittal dated February 11, 2004, page 10 of Volume IX was <br />2 <br />