2021-06-01_HYDROLOGY - M1977436 - Laserfiche WebLink

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Aggregate Industries South Platte Combined SWSP June 1, 2021 Plan IDs 3614, 4773, 3624, 4772, 4616, 3437, 3376, 3650, 3668, 5475, 5829, 8t 6090 Page 3 of 23 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. Depletions covered by this SWSP are limited to lagged depletions from past operations at the site, including past dewatering. 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 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 Status: Aggregate intends to continue actively mining the Tucson South Pit Pit during 2021. Depletions covered by this SWSP include water lost due to (South Platte evaporation, aggregate production, and dust control. Mainstem) Exposed Groundwater Surface: 10.0 acres (including 2.0 acres transferred from the Tucson Pit) Active Dewatering: Proposed to start in 2021 Wottenberq Pit Status: Resource extraction at the Wattenberg Pit is complete and reclamation (South Platte is in progress. Depletions covered by this SWSP include water lost due to Mainstem) evaporation, dust control, and dewatering. Prior to 2018, the north pit was dewatered with water delivered to the nearby Broda Pond. The north cell has since been lined, and dewatering operations have shifted to the south cell with water to be discharged to multiple locations. A portion of the water will be pumped to the Stillwater Ski Lake located south of the pit to mitigate lower levels in the pond due to the suppressed water table resulting from dewatering. A portion of the water may be pumped to a new recharge pond on the west side of the site in order to mitigate low water table levels in domestic wells in the area. A portion of the water may be discharged to the Huett Seep, a surface drainage adjacent to the site. The remainder of the dewatering discharge will be pumped across the South Platte River to the Broda Pond located within the Platte Valley Pit. Once water enters the Broda Pond, some is pumped to the river to ensure the pond does not spill. There was a temporary cessation of dewatering in January 2018. The site will be dewatered continuously throughout 2021. Exposed Groundwater Surface: 37.0 acres Active Dewatering: Yes