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Chavers Mining Resource Groundwater Monitoring and Mitigation Plan January 2024 Page 3 Site,there are multiple other factors present which impact the hydrologic balance in the area(e.g., other sand and gravel mines, slurry walls,and/or lined water storage).No wells are located within 600 feet of the dewatering pump location at the Site east of the South Platte River. Due to a lack of groundwater elevations prior to the industrial development of the area and the start of pumping at the Site,the extent of impacts to the hydrologic balance at and beyond the Site boundaries cannot be determined.ASCI will continue to monitor groundwater levels at the Site boundaries to identify any potential adverse off-site impact to the hydrologic balance when compared against data collected during the baseline characterization period. 2.3 BASELINE GROUNDWATER QUALITY 2.3.1 Groundwater Quality Standards The objective of the baseline groundwater sampling was to document the baseline groundwater quality for applicable analytes and establish the groundwater quality standards for the Site. Per WQCC Regulation No. 42 "Site-specific Water Quality Classifications and Standards for Groundwater", the Site is located within the specified area of the City of Fort Lupton Wellfield. The groundwater classifications in this area are Domestic Use-Quality and Agricultural Use- Quality. The groundwater quality standards assigned to confined and unconfined groundwater in the City of Fort Lupton Wellfield are WQCC Regulation 41 Interim Narrative Standards (INS) Tables 1 —4 (5 CCR 1002-41). These are the same standards presented in the DRMS guidance document "Groundwater Monitoring: Sampling and Analysis Plan Guidance, Construction Materials and Hard Rock Sites" (DRMS, September 2023). Per Rule 3.1.7(2)(c)(ii) and through correspondence with DRMS, the lowest WQCC Regulation 41 INS Tables I — 4 standard for applicable analytes is utilized as the default numeric protection value benchmark(i.e.,groundwater quality standard), except for analytes where the baseline groundwater concentration exceed these values. For these analytes, the highest concentration reported during the baseline groundwater sampling period is be used as a site-specific groundwater quality standard. A complete list of the groundwater quality standards for the Site is presented in Table 2. These standards will be used for comparison against future groundwater sampling event results to demonstrate protection of existing and reasonably potential future uses of groundwater throughout the operational life of the mine until reclamation has been achieved (i.e., when release of reclamation liability occurs). Any change to the analytes on the list(e.g.,reduction of analytes)or groundwater quality standard values will be submitted to DRMS via Technical Revision for approval prior to implementing. 2.3.2 Baseline Groundwater Quality Sampling Results Results of the eight (8) quarters of baseline groundwater sampling events used to determine the groundwater quality standards for the Site are presented in Tables 3 and 4. Results are compared against the lowest WQCC Regulation 41 INS Tables 1 —4 standards for applicable analytes. As shown in Tables 3 and 4, results for two (2) analytes during the baseline monitoring period (Manganese and Sulfate) exceeded the lowest WQCC Regulation 41 INS Tables I —4 standards. Therefore, the highest concentration reported for Manganese and Sulfate during the eight (8)