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Rifle Gravel Pit #1 .January 2021 !Arnendment to File No M-2020-008) <br /> shows the estimated drawdown following one-year of dewatering using 3 wells in the vicinity <br /> of the Stage 1 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 /> Water depletions will occur during mining operations from water lost with mined aggregate <br /> and water used for dust suppression. On-site sourced water will not be used for potable <br /> water demands. After mining is completed water depletions from the pit will be solely from <br /> evaporation of the exposed groundwater in the finished gravel pit pond. <br /> Augmentation of the exposed and captured groundwater is required per Colorado's Revised <br /> Statutes to protect downstream senior water right holders and will be addressed by SCI prior <br /> to subsurface mining. <br /> 8.2 Aquifers <br /> The groundwater aquifer/water table depth across the site varies from 3 feet to 8 feet below <br /> the surface. The aquifer is alluvial in nature and connected to the Colorado River. See <br /> Attachment B for information regarding the water depths at five boring locations. <br /> 8.3 Groundwater <br /> It is anticipated that the dewatering activities prior to mining will limit the exposure of <br /> groundwater and thus loss of groundwater to evaporation, during mining. The potential for <br /> this exposure of groundwater, however, will necessitate augmentation for the life of the <br /> operation. Augmentation —via a decreed augmentation plan or a substitute water supply <br /> plan (SWSP) —will be in place with the SEO prior to beginning subsurface mining activities <br /> to prevent potential injury to downstream water rights. The depletions from any captured or <br /> exposed groundwater from the Rifle Pit mining operations will have to be replaced in time, <br /> amount, and location during times of a downstream senior call. <br /> Evaporation from the post-mining finished pond will require a decreed augmentation plan. <br /> Active mining operations may be covered by the same augmentation plan or may <br /> temporarily be covered by an SWSP. SCI will file a Water Court application or contract with <br /> West Divide Water Conservancy District (or similar agency) under their decreed umbrella <br /> protection plan for an augmentation plan to replace depletions from the Rifle Pit operations <br /> (after active mining operations and potentially during active mining operations). The process <br /> of obtaining a project specific court-approved decreed augmentation plan can take from 1-3 <br /> years, depending on negotiations with the Division of Water Resources (DWR - SEO) and <br /> any potential opposers. Therefore, SCI will also file an application for a SWSP which will <br /> allow the gravel pit to operate without causing injury to other water rights holders before a <br /> final decree is entered, with temporary approval from the SEO. An SWSP can only be <br /> 30 <br />