2021-08-03_HYDROLOGY - M2017032 - Laserfiche WebLink

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Paul 131RIss August 3, 2021 Page 2o obligations previously incurred by Valco are incorporated into this SWSP and are shown in Table 2 (attached). Permit No. 84755-F (WDID 1706635) was issued for the 22 West Pit for exposure of groundwater, product retention, and dust suppression. In accordance with the letter dated April 30, 2010 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 the operator provide information to DRMS to demonstrate the replacement of long term injurious stream depletions that result from mining related exposure of groundwater. In accordance with said letter, the Applicant has dedicated the following water rights for long-term replacement of evaporative depletions resulting from exposure of 15 acres of ground water by letter dated August 30, 2018, attached. Water Right Shares Estimated Yield Total Yield (af/yr/share) (af/yr) Rocky Ford Ditch Company 2 12.86 25.72 Catlin Canal Company 15 1.54 23.10 Twin Lakes Reservoir and Canal 17.45 0.70 12.22 Company Total - - 61.04 DEPLETIONS Deep Cut commenced active mining at the 22 West Pit location in 2018; previously it was scheduled for remediation. The previously incurred lagged depletions were calculated by re-establishing the centroid for Ponds 1 and 2 and lagging the depletions using the same methodology from previous Rocky Ford Pit SWSPs. The depletions calculated in this manner total 0.64 acre-feet during this SWSP approval period (see attached Table 2). Depletions as a result of evaporation and mining activities during this plan year are shown in Table 1 (attached). Dust control is fully consumptive and has been estimated to be 1.0 acre-foot per plan year. The maximum water removed with product, assuming 20,000 tons of product removed, total 0.59 acre-feet annually. The current surface area of groundwater exposed after 1980 is identified as 9.8 acres. During the period of this SWSP, additional groundwater may be exposed, so evaporative depletions were estimated using a maximum exposed surface area of 13.2 acres. Evaporative depletions were estimated using the same net evaporation rate as previous Rocky Ford East Pit SWSPs (3.85 feet/acre/year) and total 50.82 acre feet annually. These values were lagged using a Glover analysis with the parameters as given below: Distance from river: 3,520 ft Distance from alluvial boundary: 7,670 ft Transmissivity: 71,000 gpd/ft Specific yield: 0.2