2022-12-19_HYDROLOGY - M2008082 - Laserfiche WebLink

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Morton Lakes Substitute Water Supply Plan Renewal Page 4 of 9 December 16, 2022 Dewatering Minimal dewatering will occur in Stages 5, 6D, and 7A from within the lined pits and such water is returned directly to the stream. Dewatering will occur at this site at a relatively constant rate until the end of the SWSP period. All dewatering will be accurately metered so as to properly determine the lagged dewatering depletions to the stream that will result once dewatering ceases. As long as all water is pumped from within the lined pits and is returned to the stream without consumptive use there are no new lagged depletions from dewatering that need to be replaced under this SWSP for Stages 5, 6D, and 7A. Lagged depletions from past dewatering in Stage 6C total 56.53 acre-feet as shown in Table 2, Column 6 and will be replaced under this SWSP. Additional Refill of Stage 2 It is projected that the refill of Stage 2 for storage (for subsequent dust suppression uses) will require 80.0 acre-feet of water during 2023. Since water will be pumped directly from the stream for storage (re- fill) in Stage 2, no lagged depletions will occur from this use. Slurry Wall Construction Construction of the slurry wall at Stage 7A is anticipated to begin in 2023. It has been estimated that depletions from use of water for construction of the slurry wall will be 16.11 acre-feet during 2023. In the design and construction of the slurry wall, the Applicant should consider whether drainage structures are needed to allow water to flow back to the stream and to prevent water mounding behind the slurry wall. In the vicinity of the liner, there are recharge projects and other water rights that could be affected if water cannot return to the river. Total Consumptive Use (Unlagged Depletions) The total consumptive use at the site for this plan period is 290.68 acre-feet, as shown on attached Table 2, Column 9. Lagged Depletions The IDS AWAS stream depletion model was used to determine the lagged depletions from dewatering, evaporation, and operational losses at the Morton-Holton Lakes site to Big Dry Creek and the South Platte River, using the following Glover parameters: • Specific yield = 0.2 • Transmissivity = 150,000 gpd/ft based on pumping test data in Colorado Ground Water Circular No. 11 • Distance from centroid of the Stage 1 mining area to Big Dry Creek = 300 feet • Distance from centroid of the Stage 2 mining area to Big Dry Creek = 1,150 feet • Distance from centroid of the Stage 5 mining area to Big Dry Creek = 318 feet • Distance from centroid of the Stage 6A mining area to the Big Dry Creek = 1,356 feet • Distance from centroid of the Stage 6B mining area to the Big Dry Creek = 1,724 feet • Distance from centroid of the Stage 6C/6D mining area to South Platte River = 643 feet • Distance from centroid of the Stage 6E mining area to the Big Dry Creek = 1,198 feet • Distance from centroid of the Stage 7A mining area to Big Dry Creek = 665 feet • Distance from alluvial boundary (based upon CDSS South Platte River alluvial aquifer boundary mapping o 7,250 feet for Stage 1 and 2