2024-11-14_HYDROLOGY - M2001085 (2)

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2023-2024 GSL Sand 6t Gravel Substitute Water Supply Plan Page 2 of 9 November 14, 2024 was valid through October 31, 2024. The required fee of $257 for this renewal of the SWSP has been submitted (receipt number 10038654). Plan Operation This SWSP covers depletions at the GSL Sand and Gravel Mine, generally located in the S '/z of the SW '/ of Section 35, Township 1 South, Range 67 West of the Sixth P.M. Mining operations were completed in November 2011 and a slurry wall was installed around the pond. However, the liner is not functional, therefore the Applicant requested an amendment to the mining permit to the Division of Reclamation Mining and Safety ("DRMS") to allow for backfilling of the pit. Since February 2012 when the exposed surface area was 26.7 acres, the Applicant has been working on backfilling the pond and the exposed groundwater surface area as of June 2024 was 0.86 acres. Depletions during this SWSP period consist of evaporative depletions from the exposed groundwater surface. Replacement water is fully consumable water leased from the City of Aurora ("Aurora") which will be released upstream of the pit. Depletions The depletions at the site during the period of this SWSP consist of evaporation from exposed groundwater since the lagged depletions from prior mining operations no longer have an effect on the stream. Other than evaporation from the exposed groundwater surface, no new operating depletions will occur during this SWSP approval period. The current total exposed groundwater surface area at this site is 0.86 acres. For the purposes of this SWSP, it is assumed that the exposed groundwater at the site will remain at 0.86 acres. Net evaporation is defined as gross evaporation less the consumptive use of water by vegetation that naturally occurred at the site prior to mining activity. The historical consumptive use was assumed to be equal to the effective precipitation, which was estimated based on the data from the Denver Stapleton Station. Net evaporative 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