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Morton Lakes Substitute Water Supply Plan Renewal (Amended) <br /> July 21, 2025 <br /> Page 3 of 17 <br /> to begin in December 2025, which will reduce the area of exposed groundwater to 2 <br /> acres. <br /> • Stage 3 - Mining at Stage 3 was completed in early 2018. Stage 3 was completely <br /> backfilled in the spring of 2019 with overburden from other stages. There are no <br /> remaining lagged depletions associated with this Stage that need to be replaced <br /> (which includes what was previously called Stage 3B). <br /> • Stage 4 - Mining at Stage 4 was completed in the spring of 2021 . A slurry wall was <br /> constructed around Stage 4 and a 90-day leak test was provisionally approved on May <br /> 23, 2018. Brannan completed the final construction to convert Stage 4 into its <br /> intended and approved post-mining reservoir storage use in 2021, and the final leak <br /> test was approved on May 24, 2021. On July 1, 2021 the structure was transferred to <br /> United Water. Brannan is no longer responsible for Stage 4, and any lagged depletions <br /> from previous mining of this stage and new depletions associated with future use at <br /> Stage 4 are not included in this SWSP renewal request. <br /> • Stage 5 - A slurry wall was constructed in July 2020 for Stage 5 and mining began at <br /> the end of 2020. A 90-day leak test was provisionally approved on January 5, 2021. <br /> During heavy rains in Spring 2023, Stage 5 intercepted a substantial amount of surface <br /> water from Big Dry Creek. Brannan reported that the additional water was pumped <br /> out of this stage as quickly as possible. Mining at Stage 5 was anticipated to be <br /> completed by the end of 2024, however, additional mining reserves currently remain <br /> at Stage 5 and will be mined during reservoir construction as part of this amended <br /> plan period. Stage 5 will ultimately be converted to a reservoir for post-mining water <br /> storage, which was originally planned to be completed sometime in the first half of <br /> 2025. Final construction of the Stage 5 reservoir has been delayed, and is now <br /> estimated to begin in July 2025 and last through December 2025. This will result in <br /> construction depletions that were not included in the current approved SWSP. The <br /> surface area of Stage 5 will remain at 1 acre during 2025. For the Stage 5 structure to <br /> be approved as a reservoir capable of post-mining water storage, the operator must <br /> perform a final leak test once mining is complete, and the site is at final grade. <br /> Depletions from this stage result from evaporation, dewatering, gravel production, <br />