Laserfiche WebLink
Forrest Luke <br />Page 3 of 4 <br />17 April 2020 <br />6b. Please provide appropriate maps and cross section drawings for the N Pit temporary spoil <br />pile. <br />Trapper Response 1: A recently completed geotechnical study by Agapito Associates, Inc. demonstrates <br />that Trapper's proposed temporary overburden storage dump satisfies the performance standards of Rule <br />4.14.1 (2) (e)& (h), 4.14.2 (1), and 4.09 and 4.10. Enclosed are revised permit pages 3-15c referencing <br />the results of the AAI study that determine the proposed spoil pile is likely to be stable over its projected <br />life of 4- 6 years. <br />2020 March DRMS: Per this section of the Rule, "[t]he results of a geotechnical investigation of the <br />proposed disposal area... " is required. It appears that Agapito Associates, Inc. has prepared a geotechnical <br />study to assess the global stability of the proposed spoil pile however, it does not appear that it was <br />provided with TR-124. <br />7. To demonstrate that the temporary storage will meet performance standards please <br />provide the associated geotechnical investigation for the proposed N Pit temporary <br />spoil pile. <br />Trapper Response 2 (2020 April 1): The Agapito geotechnical investigation of the N Pit <br />temporary out of pit spoil dump has been forwarded to you. Trapper would respectfully point out <br />that temporary spoil dumps are not covered by the regulations listed above. In good faith Trapper <br />completed the geotechnical evaluation to demonstrate that the pile will be stable during its <br />expected 4 — 6-year life span. <br />2020 April 17 DRMS: <br />Trapper has provided the geotechnical investigation (Report) performed by Agapito Associates, <br />Inc. (AAI) for the proposed N Pit temporary spoil pile. DRMS has reviewed the report. The <br />Report, states that "[n]umerical modeling results indicate that the proposed spoil pile geometry is <br />likely to be stable over the anticipated storage period (4-6 years)." The information in the Report <br />supports this statement. However, as required by Rule 4.09.1(7), excess spoil shall be placed to <br />ensure a long-term static safety factor of 1.5. It appears that there is no discussion or provided <br />results in the Report that specifically states that a minimum safety factor of 1.5 for the entire <br />spoil pile is met. <br />7a. Please provide additional information demonstrating that the NPit temporary spoil <br />pile meets the minimum criteria of a safety factor of 1.5 per Rule 4.09.1(7). <br />Rule 4.09.1— Disposal of Excess Spoil, General Requirements <br />2020 April 17 DRMS: <br />Excess spoil is proposed to be hauled to the A Pit ash dump area for final cover above the ash spoils. <br />Trapper proposes that approximately 800, 000 cubic yards of material be taken from the N Pit to backfill <br />the area to the approvedpost mining topography (PMT). Trapper estimates that the re -disturbance ofspoil <br />DRMS ADQ 3 TR124 17 April 2020 <br />Prepared by: R. Reilley <br />