2024-06-18_HYDROLOGY - M1977436 - Laserfiche WebLink

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Holcim South Platte Combined SWSP June 18, 2024 Plan IDs 3614, 4773, 3624, 4772, 4616, 3437, 3376, 3650, 3668, 5475, 5829, i± 6243 Page 3 of 26 Exposed Groundwater Surface: 4.5 acres post-81, 14.7 acres pre-81 Active Dewatering: No Hazeltine Pit Status: Resource extraction at the Hazeltine Pit has been completed and (South Platte reclamation is in progress. The Hazeltine Pit was lined with a soil bentonite Mainstem) slurry wall, and was approved as having been lined to the design standard referenced in the August 1999 State Engineer Guidelines for Lining Criteria for Gravel Pits in a letter dated May 25, 2016. The construction of the slurry wall resulted in groundwater mounding and flooding of adjacent property. The operator has installed a gravity drain to dewater the site on a continuous basis. A 45-day leak test was performed after installation of the permanent drain to verify that the liner was not impacted. The liner was re-approved in a letter dated March 22, 2018. The Applicant was required to install and operate the Orr Drain to reduce mounding of groundwater associated with the installation of the slurry wall at the site. According to the Applicant, the Orr Drain must continue to operate until the DRMS Permit is released. The Orr Drain currently intercepts groundwater seepage and surface flow in the Bull Seep, which are routed into the lined pit and subsequently pumped out to the Bull Seep and discharged to the South Platte River; the monthly difference between what is measured entering the pit and what is measured being pumped out is considered a depletion. Responsibilities for the Orr Drain have transferred over to the City of Thornton and will be included in their plan for augmentation decreed in case no. 18CW3158. January 2023 was the last month that depletions due to the Orr Drain were replaced under this SWSR Exposed Groundwater Surface: None Active Dewatering: No Brighton Pit Status: Resource extraction at the Brighton Pit is complete and reclamation is in (South Platte progress. Depletions covered by this SWSP include water lost due to evaporation Mainstem) and post-pumping dewatering depletions. The south and central reservoirs are lined with a slurry wall (WDIDs 0203031 and 0203385) and have obtained SEO liner approval. Reclamation work includes backfilling the remaining exposed areas, of which 2.0 acres was backfilled in 2020. Mining operations will not be considered to have ceased until the backfilling is complete. Exposed Groundwater Surface: 1.0 acres Active Dewatering: No Tucson South Pit Status: Holcim intends to continue actively mining the Tucson South Pit during (South Platte 2024. Depletions covered by this SWSP include water lost due to evaporation, Mainstem) aggregate production, slurry wall construction, landscape irrigation, and dust control. Exposed Groundwater Surface: 3.0 acres (including 2.0 acres transferred from the Tucson Pit) Active Dewatering: Yes