2013-11-29_REPORT - C1980007 - Laserfiche WebLink

Home Browse Search

Interoffice Memorandum To: Jim Stark From: Zach Trujillo Subject: West Elk— Refuse Pile Details Date: 11/29/2013 Jim — I have completed my review of the West Elk Mine refuse piles. On November 8, 2013, we took measurements of the Refuse Pile Expansion (RPE), the Refuse Pile Expansion - East (RPEE) and their associated structures. Clean water and refuse pile ditches were measured for percent slope, width and depth. Width, length and percent slope measurements were taken of the RPEE buttress. Compacted refuse was measured for slope only for both RPE and RPEE. Ditches A total of five locations were measured along both ditches beginning at the inlet of the "1/2 culvert" moving upslope to the base of the RPEE buttress. The clean water and refuse ditches run parallel to each other and measurements were taken for both ditches at the same location up the length of the slope. Table 1 shows the measurements and the location based on distance from the inlet of the "1/2 culvert" to the clean water and refuse ditch. Percent slope was measured using a rangefinder. Each ditch is based off of typical design within the West Elk permit. Within the permit, the minimum design criteria are defined for the clean water division ditch in the 'typicals' which is shown in Table 2. However, the refuse pile ditch dimensions are not as defined within the typical drawings provided in the permit. The minimum dimensions compiled in Table 2 for the refuse pile ditch is taken from the SEDCAD input variables for a 100 yr. — 24 hr. storm. It is assumed that these are the minimum dimensions for the refuse ditch to successfully pass a storm event of that magnitude. Percent slope was also taken from the SEDCAD input variables for the refuse pile ditch. 20% was used and so it is assumed the permitted average percent slope for the length of the refuse ditch is 20 %. Also, because the clean water and refuse pile ditches run parallel within the same drainage, it was assumed the average percent slope for the length of the clean water ditch is 20 %. If you compare Table 1 to Table 2, you can see each measured ditch dimensions for both the refuse pile and the clean water both meet the minimum design criteria. For percent slope, the field measured slope is comparable to that which is used within the permit. The difference in slope is most likely due to human error with the rangefinder. RPEE Buttress The RPEE buttress is permitted to be constructed in phases depending on the elevation and amount of refuse placement [Phase 1 (A and B), Phase 2 and Phase 3]. Currently, the RPEE buttress is between the Phase 1A and Phase 113 part of construction. The buttress rockfill and compacted colluvium fill placement are currently still ongoing. Table 3 compares our measurements to the final constructed dimensions of Phase 1 for the RPEE buttress.