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GSL Sand St Gravel Substitute Water Supply Plan Page 2 of 5 <br /> December 19, 2022 <br /> SWSP, it is assumed that the exposed groundwater at the site will remain at 0.12 acres. Net evaporation is <br /> defined as gross evaporation less the consumptive use of water by vegetation that naturally occurred at the <br /> site prior to mining activity. The historical consumptive use was assumed to be equal to the effective <br /> precipitation, which was estimated based on the data from the Denver Stapleton Station. Net evaporative <br /> depletions were calculated using a gross annual evaporation of 45 inches from the exposed water surface <br /> based on the NOAA Technical Report NWS 33, with a credit of 10.8 inches for effective precipitation, as <br /> shown on attached Table 1. The net depletion of groundwater due to evaporation of groundwater exposed <br /> at the site has been calculated to be 2.86 acre-feet per acre or 0.35 acre-feet for this SWSP period. A <br /> summary of the mining depletions are shown on attached Table 2. <br /> The Integrated Decision Support Group Alluvial Water Accounting System ("IDS-AWAS") model was used with <br /> the alluvial aquifer boundary condition option to lag depletions to the South Platte River. The following <br /> parameters were used in the model: <br /> Table A. IDS-AWAS parameters. <br /> X - Dist to river W- Boundary Harmonic <br /> Location (feet) Dist (feet) Transmissivity Specific yield <br /> (gpd/ft) <br /> Gravel Mine (mining and 2,295 3,836 63,000 0.2 <br /> dewatering depletions) <br /> Henderson Water Ski Lake 1,808 5,300 61,600 0.2 <br /> (recharge) <br /> Evaporative, operational losses, and dewatering depletions and accretions were considered back to January <br /> 1, 2009. Lagged evaporative and operational depletions are 0.71 acre-feet for this SWSP period, as <br /> shown on the attached Tables 3 and 4. <br /> Replacements <br /> The replacement source for this plan period is fully consumable water leased from the City of Aurora <br /> ("Aurora"). The fully consumable water will be released to the South Platte River at the outfall of the <br /> Metro Wastewater Reclamation District's Robert W. Hite treatment facility ("Metro Sewer," WDID 020070). <br /> Metro Sewer is located approximately 10.78 miles upstream of the site. As such an irrigation season (April <br /> through October) transit loss of 5.39% (0.5% per mile) and a non-irrigation season (November through March) <br /> transit loss of 2.7% (0.25% per mile) will be assessed on all releases. These transit losses are subject to <br /> change by the Water Commissioner or Division Engineer. <br /> A copy of the signed lease agreement dated November 24, 2020 is attached. The term of the lease is for <br /> the period of November 1, 2020 through October 31, 2021 and is renewable for up to five additional one- <br /> year extensions provided by written notification from Aurora. According to the attached letter from Aurora <br /> (Aurora lease extension) dated October 11, 2022, a one year extension has been granted for the period of <br /> November 1, 2022 through October 31, 2023. The proposed replacement schedule is provided in Exhibit A <br /> of the delivery schedule provided with the Aurora lease extension. Total replacements to be provided by <br /> Aurora under the lease are 1.32 acre-feet, which accounts for transit losses, during this SWSP period. <br /> Long-term Depletions <br /> The final reclamation plan for DRMS Mining Permit No. M-2001-085 once had been to create a water storage <br /> reservoir through the installation of a slurry wall. The slurry wall was constructed but did not receive its <br /> liner approval from DWR. Based on the Applicant's statements, the slurry wall leaked in multiple locations <br /> and the pit filled completely with groundwater. This was not in accordance with their DRMS permit <br />