2023-10-30_HYDROLOGY - M2001085 (2)

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2023-2024 GSL Sand St Gravel Substitute Water Supply Plan Page 2 of 5 October 30, 2023 depletions were calculated using a gross annual evaporation of 45 inches from the exposed water surface based on the NOAA Technical Report NWS 33, with a credit of 10.78 inches for effective precipitation, as shown on attached Table 1. The net depletion of groundwater due to evaporation of groundwater exposed at the site has been calculated to be 2.85 acre-feet per acre or 2.60 acre-feet for this SWSP period. A summary of the mining depletions are shown on attached Table 2. The Integrated Decision Support Group Alluvial Water Accounting System ("IDS-AWAS") model was used with the alluvial aquifer boundary condition to lag depletions to the South Platte River. The following parameters were used in the model: Table A. IDS-AWAS pararneters. X- Dist to river W - Boundary Dist Harmonic Location (feet) (feet) Transmissivity Specific yield (gpd/ft) Gravel Mine 2,295 3,836 63,000 0.2 Lagged evaporative depletions are 2.45 acre-feet for this SWSP period, as shown on the attached Tables 3 and 4. Replacements The replacement source for this plan period is fully consumable water leased from the City of Aurora ("Aurora"). The fully consumable water will be released to the South Platte River at the outfall of the Metro Wastewater Reclamation District's Robert W. Hite treatment facility("Metro Sewer,"WDID 020070). Metro Sewer is located approximately 10.78 miles upstream of the site. As such, an irrigation season (April through October)transit loss of 5.39% (0.5% per mile) and a non-irrigation season (Novemberthrough March)transit loss of 2.7% (0.25% per mile) will be assessed on all releases. These transit losses are subject to change by the Water Commissioner or Division Engineer. A copy of the signed lease agreement dated November24, 2020 is attached. The term of the lease is for the period of November 1, 2020 through October 31, 2021 and is renewable for up to five additional one- year extensions provided by written notification from Aurora. According to the attached letter from Aurora (Aurora lease extension) dated October 3, 2023, a one-year extension has been granted for the period of November 1, 2023 through October 31, 2024. The proposed replacement schedule is provided in Exh ibit A of the delivery schedule provided with the Aurora lease extension. Total replacements to be provided by Aurora under the lease are 2.55 acre-feet, which accounts for transit losses, during this SWSP period, as shown on attached Table 6. Long-term Depletions The final reclamation plan for DRMS Mining Permit No. M-2001-085 had been to create a water storage reservoir through the installation of a slurry wall. The slurry wall was constructed but did not receive its liner approval from DWR. Based on the Applicant's statements, the slurry wall leaked in multiple locations and the pit filled completely with groundwater. This was not in accordance with their DRMS permit reclamation requirements.Therefore,the Applicant obtained approval of an amendment to the reclam ation mining permit from DRMS to allow for backfilling of the pit. The current financial warranty posted for the site is $368,590, which was set by DRMS after approving an amendment request to change the reclamation plan from water storage to an inert backfill operation on the property (to two feet above the water table). This action satisfied the requirement that the Applicant diligently pursue compliance with their DRMS permit and the requirements described in the April 30, 2010 letter DRMS sent to all gravel pit operators (attached), specifically in regard to the required financial