Laserfiche WebLink
Whetstone' <br />Associates <br />.t <br />Technical Memorandum <br />1 <br />4' V <br />.,i.a <br />�f C <br />Lr ,� <br />g''sV <br />Figure 1. Satellite Image Showing Flow Direction for Stormwater exiting the PDE <br />Diversion Structure into Adjacent Subbasin B4 <br />4. Section 4.2, p. 24. Please discuss how the ephemeral pit pond is sized for pit runoff during <br />operations. <br />Cotter response: During operations, the pit will be deepened to extract overburden and <br />ore. The ephemeral pit pool will be removed to provide access for haul trucks, and the <br />access ramp will pass through the location of the existing pit pool. There will be no <br />outlet for stormwater from the open pit (subbasins D1 and DP1) during mining. <br />Instead, any stormwater that collects in the pit during operations will be collected in the <br />floor of the pit and handled appropriately in accordance with the EPP. <br />S. Section 4.7, p.42. Losses due to channel infiltration during a 100 year design storm are <br />generally considered to be negligible. Please justify the use of channel infiltration in the <br />HydroCAD® models. <br />Cotter response: Infiltration losses are only applied to standing ponds and channels <br />along the valley floor in the stormwater runoff modeling for the JD -7 Mine. The <br />justification for infiltration losses in alluvial fans and along mountain front terrains is <br />described in research papers for the and southwest (Tillery, USGS, 1990). Infiltration <br />losses, while significant, constitute only a small percentage of the runoff from the 100 -yr <br />storm. Stormwater reports to the drainages within hours of the onset of precipitation <br />and the peak runoff occurs at approximately 12 hours. Infiltration losses in the high- <br />4149A.140207 6 <br />