2023-10-03_REVISION - M1977344 (31)

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Bear Creek Quarry (M-1977-344) Permit Amendment Holcim US Inc, 3500 Highway 120, Florence, CO 81226 Phone (719) 288-1443 www.holcim.us 65 2.7.3 Site Investigations and Characterization Five groundwater monitoring wells were installed both to the north and south of Red Creek in November 2021. The objective of the well locations was to assess the groundwater elevations near the surface water seeps observed in the Red Creek drainage. The wells were located upstream and downstream of the seep and within approximately 400 feet of the Red Creek canyon edge. Wells were spaced to ensure the data collected from each well was spatially distributed in order to characterize the hydrologic properties of the water bearing units. The monitoring well permits are provided in Appendix 4.3 A stilling well was installed along the north side of Red Creek to measure water levels within the saturated alluvium of the creek bed as a proxy measurement of the creek water elevation. The stilling well was drilled using an auger to advance a hole to approximately five feet below ground surface. A five-foot polyvinylchloride (PVC) slotted screen with an end capped was placed into the hole then sand was backfilled in the wellbore up to the surface. Transducers were installed after development operations in Well 1, Well 2N, Well 2S, Well 3, Well 4, and the Stilling Well to continuously monitor the groundwater levels. Immediately prior to transducer installation, a depth-to water measurement was collected to establish a value between transducer measurement and elevation. Coordinate and elevation data were collected by Holcim for each well casing and adjacent ground surface using survey equipment. A surface water flow monitoring station consisting of a ramp flume designed to measure flow between 0.1 to 3.5 cubic feet per second (cfs) was installed in August 2022. The location of the flume was selected based on a visual reconnaissance of the stream and the proximity to the surface water seeps . The Sampling and Analysis Plan (SAP) was implemented during the baseline monitoring and sampling activities. This SAP is designed to collect data to assess potential water resource impacts from mining operations conducted at the RCQ. Constituent loading to surface water and groundwater could occur during mining operations from stormwater runoff or groundwater seepage into mine pits. The SAP establishes methods that will obtain accurate and defensible data by following site-specific and standard operating procedures (SOP). The SAP, provided in Appendix 4.4, will be implemented for all water monitoring and sampling activities during the life of RCQ. In conjunction with the SAP, the Quality Assurance Project Plan (QAPP) was developed and implemented during the baseline investigation. It is provided in its entirety in Appendix 4.4. The QAPP describes quality assurance/quality control (QA/QC) procedures that will be followed during implementation of the surface water and groundwater data collection. QA is a management function and refers to the systematic planning of procedures, methods, and standards to ensure that data generated by the testing program are suitable for their intended use. QC is process-oriented and focuses on error identification and verification that data meet the established standards. The standards contained in the QAPP will be used for verification and validation of data generated by field personnel and laboratory subcontractors. The QAPP is intended to serve as a guide to field personnel and laboratory subcontractors for QC activities during the monitoring and reporting phases of this project. Specific details for sampling and analyses are provided in the RCQ Baseline Monitoring SAP and SOPs. 2.7.3.1 Groundwater and Surface Water Baseline Study In a pre-application meeting, DRMS stated five quarterly monitoring events would be required to compile the necessary data to establish baseline water quality. 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. The Red Creek Quarry Baseline Water Investigation is provided in its entirety in Appendix 4.5.