2016-09-09_REVISION - M1987113 (3)

Home Browse Search

Environment, Inc. Page 2 Bestway Concrete-Rocky Flats Pit M-1987-113 September 9,2016 The decision was made to operate the mine under the existing approved permit and at a later date to reapply for the ditch relocation if it is appropriate. Therefore the Technical Revision to move the ditches is withdrawn. 4. What offsets will be maintained between the limit of mining and the relocated ditches? The map has been revised to show the setback dimensions around the mine. The dig line in the original approval is approximately 30 to 50 feet for the center line of each respective ditch as described on page 6 of the 1987 application book. 5. The Reclamation Plan Map shows the pit walls will be reclaimed at 2H:1 V. The currently approved final grade of the pit walls is 31-11:IV. In Technical Revision No.1, the Operator acknowledged that it would be difficult to establish vegetation on a 21-1: IV slope and changed the final grade to 3H:1 V. The Division concurs that establishing vegetation on 21-11: IV slope is difficult. In addition, a 21-1: IV slope would not be commensurate with the approved post-mining land use of pastureland. The Technical Revision narrative does not discuss changing the final grade of the pit walls. Please revise the Reclamation Plan to depict the approved final grade of the pit walls. If the Operator wishes to change the final grade to 21-1:1 V, then provide a technical justification for this change and explain how vegetation will be successfully established on this slope. You are correct. The 2004 map was correct and the new slope left along the backfilled area on the south, is labeled and drawn at 3h:ly. 6. The Operator is proposing to mine deeper than what is currently approved, but does not specify the maximum depth in text. The Reclamation Plan Map shows the deepest part of the pit will be at an elevation of 6030'. Please confirm this is the maximum depth to which the pit will be mined. I can't state the final known floor elevation because we do not know how deep the reserve is on this site. The test holes the DOE did in the 1970 's were never drilled to the bottom of the Rocky Flats alluvium on this site so we are unsure how deep it goes. The. deepest monitoring well drilled by DOE, on the east side, was 100 feet and it did not reached bedrock. We also do not know if there is clay under the gravel as noted on page 7 of the original application book. It is drawn at the depth shown on the maps because some bottom elevation has to be shown, but we do not know how deep it will eventually be mined. The intent has always been to mine as deep as possible with the hopes that clay will be found under the alluvial deposit. It that is the case then the plan would be to chase the clay as deep as it is safe to do so or the bottom of the deposit is reached. So the maps show the minimum depth and we intend to maximize removal of the resource. 7. The Operator is proposing to mine the pit deeper. In Technical Revision No. 1, the Operator states the limiting factor to the depth of mining is groundwater which occurs at approximately