2024-01-29_HYDROLOGY - M2001107 - Laserfiche WebLink

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NCCI Pit#1 Substitute Water Supply Plan Page 2 of 4 January 29, 2024 and dewatering that occurred prior to the liner approval in November 2023. Unlagged evaporative and dewatering depletions from 2023 were 852.5 acre-feet as shown on attached Table 1. The IDS AWAS stream depletion model was used to determine the lagged depletions to the South Platte River caused by the NCCI #1 Pit. The following parameters were used in the model: Transmissivity (T) _ 150,000 gallons per day per foot; Specific yield (SY) = 0.2; Distance from the South Platte River to the edge of the alluvium (W) = 5,000 feet; and Distance from the centroid of the exposed surface water areas to the South Platte River (X) = 3,300 feet. The total lagged depletions during 2024 caused by past evaporation and dewatering at the NCCI #1 Pit are estimated at 92.5 acre-feet, as shown on attached Table 2. Depletions from the mining operation accrue to the South Platte River in Section 19, Township 2 North, Range 66 West, 6th P.M. For purposes of this SWSP, the point of depletion will be considered the point where the South Platte River crosses the South line of Section 19, Township 2 North, Range 66 West, which is just upstream of the Meadow Island No. 1 Ditch. Replacements The source of replacement water is fully consumable water from Thornton. Thornton purchased the NCCI Pit#1 site for future reservoir storage and entered into an agreement (attached) allowing NCCI to continue mining the site. The agreement requires Thornton to replace depletions caused by NCCI's mining operations. The water from Thornton will be released from the Metropolitan Wastewater Treatment Plant ("Metro", WDID 0200700). Thornton is anticipated to be able to provide 107.6 acre-feet of replacement supplies in 2024. A 0.5% per mile transit loss (14% overall loss for the 28 miles between Metro and the point of depletion) was accounted for in the SWSP. Conveyance loss for delivery of augmentation water is subject to assessment and modification as determined by the Water Commissioner and/or Division Engineer. Conditions of Approval I hereby approve the proposed substitute water supply plan in accordance with section 37-90-137(11), C.R.S., subject to the following conditions: 1. This SWSP shall be valid for the period of January 1, 2024 through December 31, 2024, unless otherwise revoked or superseded by decree. If this plan will not be made absolute by a water court action by the plan's expiration date, a renewal request must be submitted to this office with the statutory fee by November 1, 2024. If a renewal request is received after the expiration date of this plan, it will be considered a request for a new SWSP and the $1,593 filing fee will apply. 2. Well Permit 74792-F has been issued for this pit, and this permit remains valid. The permit covers up to 111.14 acres of exposed surface area and dewatering activities. Since mining at the site is completed, there is no more groundwater exposed at the site and the site is lined the Applicant, shall request that the well permit no. 74792-F is canceled. 3. Approval of this plan is for the purposes as stated herein. Any use of this water must first be approved by this office. 4. The storage structure/reservoir must be equipped with outlet works capable of passing all out-of- priority inflows to the nearest natural watercourse. All out-of-priority inflows to the storage structure/reservoir from any source, including precipitation, must be released without use. 5. The Applicant shall provide daily accounting (including, but not limited to diversions, depletions, replacement sources, and river calls) on a monthly basis. The accounting must be uploaded to the CDSS Online Reporting Tool within 30 days of the end of the month for which the accounting applies (https://dwr.state.co.us/Tools/reporting). Instructions for using the tool are available on the Division of Water Resources website on the "Services" —> "Data Et Information" page under the heading of Online