2023-10-03_REVISION - M1977344 (22)

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vii DRAFT for review purposes only. Use of contents on this sheet is subject to the limitations specified at the end of this docu ment. Red Creek Quarry Baseline Water Information 20230907 Executive Summary Holcim (US), Inc. (Holcim) is submitting an amendment for the Bear Creek Quarry (BCQ) to the Colorado Division of Reclamation, Mining, & Safety (DRMS) to include mining activities for the proposed Red Creek Quarry (RCQ). The proposed RCQ will consist of an open-pit limestone quarry and conveyor corridor to provide limestone to the Holcim Portland Plant. The mining operation will develop limestone reserves from the Fort Hays and related formations in portions of Sections 24 and 25, T20S, R68W in Freemont County and Sections 19, 20, 29 and 30, T20S, R67W in Pueblo County. In a pre-application meeting, DRMS stated five quarterly monitoring events would be required to compile the necessary data to establish baseline water quality. The data and results from the five monitoring events would need to be summarized in a Baseline Characterization Report appended to the permit application. Per DRMS Rule 6.4.7 Exhibit G–Water Investigation Requirements, the amendment will need to address the impact of the mining operation on surface water and groundwater systems. Brown and Caldwell conducted a multi-year baseline investigation to document and characterize the hydrologic system at the RQC quarry site to evaluate if the proposed mining operations will result in the interception of groundwater, and to determine what if any, hydrologic connection may exist between groundwater and the Red Creek perennial surface water. Field activities conducted as part of this investigation included installation of five groundwater monitoring wells, installation of pressure transducers to collect water level data, and the collection of groundwater samples for laboratory analysis. Additional field activities included the installation of a ramp flume and stilling well transducer, visual observation and documentation of surface flow locations, and the collection of surface water samples for laboratory analysis. Groundwater modeling was conducted in support of mine permitting activities to evaluate potential groundwater impacts from planned mining operations at the RCQ. The groundwater modeling report is provided under separate cover. The results of the five quarterly surface and groundwater monitoring events identified several naturally occurring analytes present at concentrations above regulated water quality standards, including selenium, uranium, radon, and sulfate. Several groundwater and surface water studies conducted by others also found elevated concentrations of these analytes within the same lithological units and similar surface water bodies in Colorado. Water quality data suggests the source of the surface water within the perennial section of Red Creek is groundwater based on the similarities of major ion and metal concentrations. Surface water concentrations of major ions tend to fall within the ranges observed in samples collected from the groundwater wells. Variations in the water composition of the surface water samples indicate the influence of creek bed sediments, evaporation, precipitation, and multiple groundwater seeps or springs contribute to the water quality and flow in Red Creek. Groundwater modeling results indicate the future open pit will have minimal impact on the groundwater system as the pit bottom extends into the Codell Sandstone during years 0-20. However, the groundwater model indicates there will be minimal to no impact on flow within the perennial sections of Red Creek. Red Creek is intermittent and has no surface flow as it moves north from the proposed RCQ boundary, indicating mining operations will likely have no impact on the Arkansas River to the north of the site.