2022-10-26_HYDROLOGY - M2008082 - Laserfiche WebLink

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Ready Mix Concrete Substitute Water Supply Plan Page 4 of 9 October 26, 2022 Dust Suppression The estimated water used for dust suppression is 23.13 acre-feet during this plan period, as shown in Table 2, Column 5. Brannan will pump water from Stage 2 for dust suppression purposes during this plan period. Dewatering Brannan will dewater Stage 6C during the period of this SWSP. Dewatering from Stage 6C is discharges to the South Platte River. According to the Applicant 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. Stage 1 was previously dewatered, however all dewatering has ceased and there are no remaining lagged dewatering depletions from that Stage. Water pumped from Stage 2 is used for mining purposes and the depletions from such use is replaced under this SWSP. All dewatering occurring in Stages 5, 6B and 7A is from within the lined pits and such water is returned directly to the stream. As long as all water is pumped from within the lined pits and is returned to the stream without consumptive use there are no lagged depletions from dewatering that need to be replaced under this SWSP for Stages 5 and 6B. Reservoir Construction / Slurry Wall Construction of the slurry wall at Stages 7A and 7B is anticipated to begin in 2022. The amount of water that will be required for such construction, and the period of construction, are still uncertain, however the SWSP request assumes construction will begin in October 2022 and will continue through December 2022. It has been assumed that depletions from use of water for construction of the slurry wall will be 8.61 acre-feet during that period. 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 The total consumptive use at the site for this plan period is 109.09 acre-feet, as shown on attached Table 2, Column 7. 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 3B mining area to South Platte River = 700 feet