2016-07-28_PERMIT FILE - M2016010 (2)

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WORWEST ENGINEERING EVALUATION OF LTC ROAD JULY 28,2016 COR PORAT ION PAGE 7 OF 10 Increased Flooding Potential Problem: Development of the quarry could increase flows in Little Turkey Creek increasing the risk of the road flooding. Solution: Based on public comments, Little Turkey Creek already floods the road, so quarry development will not create a flooding problem. As discussed above, the quarry design includes a water management system that is designed to convey runoff from the 100-yr, 24-hr storm event through detention basins and then into Little Turkey Creek or Deadman Creek. The detention basins discharge over a 72-hour period to remove sediment and reduce peak flows. This detention period and slow release of waters minimizes changes to the creek flood hydrograph. The peak flow in the creek will have passed before the detention basins reach their peak outflow. Consequently,there will be no increase in flooding on Little Turkey Creek Road and the quarry drainage plan may reduce flooding on the road. Blocked or Washed-out Culverts Potential Problem: The quarry development could increase the risk of culverts blocking or being washed- out. Solution: Culvert failure typically occurs when the culvert is undersized or the culvert is blocked by debris. \ The conveyance capacity of the existing culverts is limited to the pipe diameter and the fill height above the culvert. Each culvert is typically designed to safely pass the peak flow from a specific design storm. As discussed above in the"increased flooding"section,the impacts to flows on Little Turkey Creek or Deadman Creek will be minimally impacted by quarry development. Also, as mentioned above in the "structure description'section,the existing culverts are undersized for the peak flows from the 10-year,24-hour storm event and as a result flooding is a common occurrence. Development of the quarry will not impact the performance of the existing culverts. Quarry development will not have any disturbances within 100 feet of the creeks, and this buffer prevents quarry operations from affecting the amount of debris in Little Turkey Creek or Deadman Creek. Rock Falls Potential Problem: Rock falls, potentially caused by blasting operations, could block the road requiring additional maintenance and repairs. There is also a concern with rock falls hitting vehicles as they travel the road. Solution: Rock falls are natural occurrences in steep terrain, particularly near cliffs of broken, faulted or jointed bedrock (CGS, 2008). Public comments suggest that rock falls are already common along Little Turkey Creek Road. These rock falls are the result of geology and topography and will continue to occur regardless of operations at the quarry.