2000-12-01_REVISION - M1977342 - Laserfiche WebLink

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MINE ID # OR PROSPECTING ID#: INSPECTION DATE: 11-14-00 M-1977-342 PAGE: 2 INSPECTOR'S INITIALS: ACS Technical Revision TR-09 to the Henderson reclamation permit describes the No. 3 Dam modifications that were undertaken at the mill during year 2000. These modifications included grouting of the abandoned No. 2 Dam decant system and rerouting of No. 3 Dam seepage to the main seep water management system located below No. 1 Dam. The decant system grouting has been completed, but the 3-Dam seepage project is being discontinued prior to completion due to the onset of winter weather. During a telephone conversation the week of November 6, 2000, the Division of Minerals and Geology discussed winterization measures for the project with Henderson personnel and contractors. The primary purpose of this inspection was to observe and document the work completed and the work remaining as approved in technical revision TR-09 and to observe and discuss winterization measures for the project. As described below, logging and topsoil projects in and around the tailing basin were also inspected. The outlet works for the dual 3-Dam seepage HDPE pipelines were inspected. The pipes enter a concrete vault equipped with knife valves located adjacent to the main seep water canal. Upon completion of the outlet works installation, 3-Dam seepage will flow from the HDPE pipelines into the canal and to the Ute Park Pump Station. The dual pipeline route was observed. Pipeline installation has been completed from the inlet structure on to the outlet structure. The pipes have been buried and the clean outs have been installed. The pipeline pressure testing has not yet been done. The collection ponds below 3-Dam were inspected. The north and south collection ponds are impounded behind dikes that abut an intervening natural rock knob. The inlet works for the dual HDPE pipelines are located in the south collection pond. Pipeline installation procedures included trenching through the south dike and salvage and stockpile of the trenched dike materials for subsequent pipeline covering and dike reconstruction. Henderson's project manager, Mike Ley, reports that the original plan had called for separate handling of the blanket of liner soil that was installed on the interior face of the dike during original construction. However, no textural or color differences were observed to indicate that the dike materials were zoned. The dike soils were sampled and tested for Proctor density and gradation. The samples were not tested for Atterberg limits. Based on the testing results, it was determined that the dike is not zoned and all of the trenched soils were stockpiled together. Trench backfilling was underway at the time of this inspection. However, a shortage of dirt and freezing conditions will prevent completion of the backfilling job this year. The dirt shortage is the result of using a portion of the soil trenched out of the dike for construction and backfilling around the new pipeline inlet works. Unusually low nighttime temperatures for November have caused the freezing conditions and resulting difficulties with frozen soils and subgrades as well as approximately one foot of snow cover. The inability to completely backfill the south dike will result in a notch remaining in the dike through the winter. There will still be substantial freeboard above the elevation of the pipeline inlet and a large amount of storage capacity in the pond. Also, the 3-Dam pump station will remain operational through the winter as a back up to the seep water pipelines. There is a thick layer of tailing deposited in the south collection pond. A layer of iron oxy-hydroxide sludge overlies the tailing. Some of this material was removed and transported to 2-Dam for disposal, but due to difficulty in excavating and trucking the soft, saturated sludge and tailing, most of it will remain in the pond.