2012-03-06_HYDROLOGY - M2001090 - Laserfiche WebLink

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River Valley Resource Pit SWSP Page 2 of 8 February 22, 2012 Phase 1A. Phase 1A includes 14.5 acres of disturbed area as shown on Figure 2 (attached). Groundwater was not previously exposed at this site. Alpine anticipates exposing groundwater in the form of a dewatering trench. In accordance with the letter dated April 30, 2010 (copy attached) from the Colorado Division of Reclamation, Mining, and Safety ( "DRMS "), all sand and gravel mining operators must comply with the requirements of the Colorado Reclamation Act and the Mineral Rules and Regulations for the protection of water resources. The April 30, 2010 letter from DRMS requires that you provide information to DRMS to demonstrate you can replace long term injurious stream depletions that result from mining related exposure of ground water. In accordance with approach no. 4, you have provided an affidavit dated December 13, 2011 that indicates that 1.38 cfs of the Suttle Ditch and 1.0 cfs of the Weiskopf Ditch water are dedicated for use as sources of replacement water solely for this SWSP for as long as there are depletions at this gravel pit site, or until such time as another replacement source is obtained. A copy of this affidavit is attached to this letter. For the purpose of this SWSP, this affidavit will be accepted for the dedication of the shares; however, if the State Engineer determines that a different affidavit or dedication process is necessary to assure proper dedication of the shares, additional information may be required prior to future SWSP approvals. Depletions The anticipated net depletions for this SWSP are 10.49 acre -feet per year. This SWSP anticipates that a total of 1 acre of water surface will be exposed at the site in the dewatering trenches around the Phase 1A mined area. You have provided a monthly breakdown of the annual depletions that include 1.94 acre -feet of net evaporative loss, 1.47 acre -feet of water lost with the mined product (which represents 100,000 tons of mined product), 3.15 acre -feet of water used for dust control, and 3.93 acre -feet used for irrigation purposes. The material will be mined below the water table in a dewatered state and will not be washed; therefore, in accordance with the State Engineer's General Guidelines for SWSPs for Sand and Gravel Pits, the assumed moisture content is 2% by weight. Water will be used to irrigate approximately 3.4 acres of berms around the Phase 1A area. For the purposes of this SWSP, you assumed that pasture grass will be the vegetation planted on the berms. The State CU model was used with the Modified Blaney - Criddle method and TR -21 crop coefficients to estimate the irrigation water requirement for pasture grass in this area with the climate data taken from the Steamboat Springs weather station over the 1911 to 2010 period. The resulting average annual irrigation water requirement is approximately 1.16 acre -feet per acre. For the 3.4 acres of berms, the total irrigation consumptive use is estimated to equal 3.93 acre -feet per year (Table 3). A stream depletion model was developed for the River Valley Resource Pit and the effects of the delayed impacts are found on the attached Table 4. The aquifer characteristics used in the •