Laserfiche WebLink
Rifle Gravel Pit #i Ma1rh ;'{ 21 <br /> Coverage under a Nationwide Permit No. 7 will also be obtained for the outfall to the <br /> Colorado River. Scott submitted a Watershed Permit Application to the City of Rifle to <br /> address the dewatering discharge within their Watershed Protection Area. <br /> Dewatering Pumping Information <br /> The rate of groundwater discharge(pumping) associated with dewatering is expected to <br /> approach about 7 cfs. Mr. Bill Hahn (Hahn Water Resources, LLC) predicted the anticipated <br /> dewatering operations (through modeling); however, this is an estimate based upon borings <br /> and groundwater level data. Mr. Hahn presented one possible dewatering configuration that <br /> might be employed for dewatering associated with the initial stages of mining. Figure 11 <br /> shows the estimated drawdown following one-year of dewatering using 3 wells in the vicinity <br /> of the Stage 1 and Stage 2 mining limits. <br /> In this case, the dewatering might be accomplished using 3 wells plus temporary drains and <br /> pumps to capture incidental inflows, pumping at a combined rate of about 3 cfs. The number <br /> and size of the dewatering pump(s)will be determined once mining commences, however, <br /> Mr. Hahn assumed the wells would be drilled to a depth of 30 feet, constructed with nominal <br /> 8-inch to 12-inch diameter casing and screen, equipped with 10 horsepower pumps and <br /> motors to pump 400 to 700 gallons per minute (gpm) and 2 to 4 centrifugal ditch pumps <br /> capable of pumping up to several hundred gpm of incidental pit inflows. <br /> The dewatering permit terms and conditions will require that this information be documented <br /> in the application. Attachment C includes a copy of Mr. Hahn's reports. <br /> 5.2.2 Mining Preparation (Phase 2) <br /> This phase of the project will include mobilization of the heavy equipment, work trailer, <br /> screening and wash equipment, and major site grading to prepare the site for mining <br /> activities. <br /> 5.2.2.1 Topsoil and Overburden Handling <br /> This phase of the project will include additional minor site grading and vegetation removal, <br /> as needed. Equipment for this phase will include, but not be limited to, a bulldozer, track- <br /> hoe, and a 35-ton haul truck. <br /> 6.2.2.2 Water Handling and Dewatering <br /> Phase 1 dewatering activities will continue throughout this phase. No additional water <br /> diversions nor impoundments will be required during this phase. <br /> 5.2.2.3 Schedule of Operations <br /> The Rifle Gravel Pit will operate from 7 am to 7 pm Monday through Friday, and weekends, <br /> as needed. Scott will limit winter operation hours between the hours of 7 a.m. and 5 p.m. <br /> Approximately 3 to 5 employees will be on site during this phase of the mining operations. <br /> No nighttime activities are anticipated. Occasional equipment repair, or maintenance may <br /> be conducted at night, but lighting will be kept to a minimum and directed inward; the site <br /> will not have ambient lighting. <br /> 19 <br />