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6.4.7. Exhibit G -Water Information <br /> (1) The operation will affect groundwater systems through evaporation and <br /> pumping. Predicted depletions to groundwater which are tributary to the Big <br /> Thompson River will be mitigated through design and implementation of a <br /> Temporary Substitute Water Supply Plan (SWSP). A well permit and <br /> associated SWSP will be acquired and approved by the Colorado Office of <br /> the State Engineer (SEO) prior to exposure of any groundwater onsite. <br /> (2) (a) Surface water structures are shown in Exhibit C1, Pre-Mining Plan Map <br /> (b) The sand and gravel deposit to be mined is an alluvial aquifer tributary to <br /> the Big Thompson River. <br /> (c) Water from dewatering operations is routed to sediment pond to allow for <br /> settling of suspended sediment. A stormwater management plan has been <br /> prepared for the site which identifies BMP's to prevent pollution to surface <br /> waters due to stormwater runoff. <br /> (3) Under full operation, the project will consume approximately 5-10 acre-ft/ <br /> year due to evaporative loss of exposed groundwater in dewatering trenches, <br /> water lost within the mined product and water consumed for dust control. <br /> (4) The replacement source for all depletions to the Big Thompson River will be <br /> either fully consumable water rights leased by the operator from the City of <br /> Loveland or other water rights owned by the operator decreed for <br /> augmentation. <br /> (5) The applicant has applied for and received a NPDES Stormwater Discharge <br /> Permit. The permit number is TBD. <br /> Hydrologic Balance <br /> Surface Water <br /> To allow prevent the empty mining cells from capturing the Big Thompson River <br /> (BTR) during a significant flooding event, flood control spillways have been <br /> designed to allow the flood to enter the empty mining cells in a controlled fashion <br /> and therefore mitigate the potential for river capture. The design theory and <br /> calculations are given below and the spillway plan and profile design drawings ae <br /> given in Exhibit F Sheets 4-11. The spillways are to be constructed immediately <br /> following excavation of a mining cell. <br /> Spillway Design <br /> The spillway design is generally based on the principals and methodology given <br /> in the Technical Review Guidelines for Gravel Mining & Water Storage Activities <br /> (TRG) published by the Urban Drainage and Flood Control District (UDFCD) in <br /> 2013. Other methods in the design include application of HEC-RAS non-steady <br /> flow modeling to verify the adequacy of the channel sizing derived from TGR <br /> methods in the largest cell. Chapter 8 of the UDFCD manual was also used for <br /> sizing the slope revetment of the spillway inlets. <br /> Amen Aggregate Resource <br /> Specific Exhibits <br /> Page 35 of 84 <br />