2024-11-22_REVISION - M1999120 (4)

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Groundwater Quality Monitoring Plan Water wells used for water level gauging are not used for groundwater quality sampling. However, the groundwater quality wells may be used for water level gauging. 3.2 Water Quality Monitoring Water quality monitoring wells are sampled on a quarterly basis for at least five consecutive quarters, Water quality samples are collected from the WQM wells listed in Table 2, in accordance with the Groundwater Sampling Plan. Water quality samples are analyzed for the parameters listed in Table 3. Approved baseline water quality parameters are included in the water quality data collection. Once baseline water quality data is obtained, all or only select number of water quality monitoring wells and parameters will be utilized for the collection of water quality data in the future. This GWMP includes parameters from the Colorado Department of Public Health and Environment (CDPHE) Reg 41 —Basic Standards for Groundwater Tables 1 through Table 4. The water quality sampling parameters are listed in Table 3 in Appendix I. LG Everist commits to obtain the water quality samples on a quarterly basis for five quarters prior to exposing water during mining. The water quality data will be used as a baseline, while subsequent water quality data, obtained annually, will be compared to the baseline data to assess water quality variations. Parameters with significant non- detects or are determined to be unrelated to mining and/or mining activities may be petitioned to be omitted during the water quality assessment and only with DRMS approval. 4.0 WATER QUAUTY EVALUATION The proposed water quality evaluation is based on statistical analysis, where the baseline data is compared to future samples. The date will be analyzed statistically to evaluate expected natural water quality variations within the aquifer. The statistical analysis is necessary to provide a means to evaluate the expected range of values in the representative baseline data, so that when future samples are obtained, variations outside the statistical norms can then be evaluated regarding the potential of water quality degradation from mining activities. 4.1 Baseline Data Collection To initially evaluate the baseline data, a normal distribution and a 95 percent confidence interval around the mean will be used to establish a baseline range of values. This is standard statistical analysis commonly used for data management to establish an anticipated range of naturally occurring values that may occur in the aquifer. Water quality changes within the baseline data could be related to (a) seasonal variations, (b) changes in precipitation recharge, (c) spatial variations within an aquifer due to heterogeneous geologic conditions and/or(d)changes in water levels and hydraulic �-,MOLEN LG Everist Fort Lupton GW Monitoring Plan a assoaA S Page 5 of 7 30