2025-04-14_HYDROLOGY - M1977436 - Laserfiche WebLink

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Holcim South Platte Combined SWSP April 14, 2025 Plan IDs 3614, 4773, 3624, 4772, 4616, 3437, 3376, 3650, 3668, 5475, 5829, &t 6243 Page 4 of 37 SWSP in 2019 and was incorporated into this SWSP starting in the 2020 plan period. Holcim never began mining at that site and no longer intends to mine it and this pit is no longer included in this SWSP. The Irwin-Thomas Pit (Plan ID 5829, WDID 0505626) operated under an individual SWSP in 2019 and was incorporated into this SWSP starting in the 2020 plan period. The DPG Pit (Plan ID 6243, WDID 0307924) operated under an individual SWSP in 2022 and 2023 and was incorporated into this SWSP starting in the 2024 plan period. A summary of the mining operations at each of the twelve (12) sites included in this SWSP is provided below. Jeronimus Pit Status: Resource extraction at the Jeronimus Pit is complete. Operations on-site include backfilling of the pit with inert fill. Depletions covered by (South Platte this SWSP are limited to water lost due to evaporation. The total surface Mainstem) area exposed at the site is 19.2 acres, of which 14.7 acres were exposed to the atmosphere prior to January 1, 1981 ("pre-1981"). The 14.7-acre area exposed at the Jeronimus Pit prior to 1981 is tied to the location as shown on the exhibit dated January 31, 2011 as provided in the 2011 SWSP. The credits for the pre-1981 area are tied to the location identified on that map and may not be re-allocated to other areas of groundwater exposure within the gravel pit permit boundary. 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 reclamation is in progress. The Hazeltine Pit was lined with a soil (South Platte bentonite slurry wall, and was approved as having been lined to the Mainstem) 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