2021-06-03_PERMIT FILE - M2021021

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Rifle Gravel Pit #1 June 2021 The existing topsoil will be stripped and used for the required berms along the perimeter of the site. These berms will be place inside of a 25-foot set back area from the property line. These berms will be roughly 5-feet in height and 23-feet wide at the bottom and will help control noise during operation. See Figure 9, Exhibit D1, for additional information regarding the topsoil and overburden handling and a cross-section of the typical mine strata. Note overburden materials across the site vary. The boring holes indicate the overburden depth can vary from 5.5 feet to 6 feet. Attachment C includes the typical cross-sections at the boring holes. 5.2.1.3 Water Handling and Dewatering Stormwater Management Scott will apply for coverage under Permit No. COR400000, Colorado Discharge Permit System (CDPS) General Permit (for) Stormwater Discharges Associated with Construction Activity at least 10 days prior to the commencement of construction activities disturbing greater than or equal to 1 acre. This permit has several requirements that address water quality and stormwater management, including monitoring and reporting, and the development and implementation of a Stormwater Management Plan (SWMP). During the initial stages of mining, Scott will not disturb the tailwater channel in its existing location and implement BMPs to prevent mining operations from discharging into or commingling with these waters. Scott will install a low-water crossing at the existing tailwater channel crossing or collect the channel in a pipe. Dewatering Scott will support the mining dewatering through temporary drains and pumps to capture incidental inflows on the pit mining floor plus 3 wells. The anticipated combined rate of pumping for these two activities was modeled at about 10 cfs. The trenching and installation of the proposed dewatering pipeline will create temporary impacts to federally jurisdictional wetlands located on the Shideler property (Parcel 217908100527), and will also require a permanent outfall structure on the bank of the Colorado River, which will constitute a permanent impact to that jurisdictional water. A range of alternatives were considered for this project and every effort was made to avoid the discharge of dredged or fill material into waters of the United States. Scott negotiated a temporary license agreement with the owner of the neighboring Shideler property (Parcel 217908100527)to the east that will allow Scott to bury a 12" dewatering pipeline that will collect and convey pumped dewatered water to the Colorado River. This pipeline will have an energy dissipation structure upstream of the discharge point to the Colorado River and an armored outfall to prevent erosion and sedimentation discharges into the Colorado River. Figure 11, Exhibit D2, shows the dewatering pipeline alignment. We want to recognize your request to provide flow arrows from the Rifle Pit to the Colorado River, however the scale of these drawings is making this detail hard to read. 17