Laserfiche WebLink
Amy Eschberger Protect No 20144265 ' <br /> Colorado Division of Reclamation, Mining and Safety July 24,2020 <br /> 3.0 MONITORING AND DATA EVALUATION ' <br /> 3.1 Monitoring <br /> After well installation, it is anticipated that at least six rounds of semi-annual groundwater monitoring (water level ' <br /> measurement and water quality sampling)will be performed. Due to the low hydraulic conductivities observed in <br /> existing monitoring wells and the responses observed post well install at MW-6 and MW-7, it is anticipated that ' <br /> the new wells may take considerable time (e.g., years) to stabilize and be reflective of in situ groundwater <br /> chemistry following the disturbance by drilling. <br /> As observed in well MW-6 and MW-7 the reported values the first few years of monitoring may not be reflective of , <br /> true aquifer conditions. If increasing or decreasing trends are observed, additional monitoring may be necessary <br /> to confirm that the water quality is representative of formation water. This determination will be made through <br /> visual assessment of time series graphs. ' <br /> This monitoring will be conducted in accordance with the procedures outlined in the Sampling and Analysis Plan <br /> (Golder 2010). The new well monitoring events will be consistent with the monitoring events for the existing wells ' <br /> so that the results will be comparable. The constituents to be analyzed for this water quality sampling will be the <br /> same as currently being conducted on a semi-annual basis for the existing wells outlined in TR-9 (Golder 2018). <br /> 3.2 Evaluation of MW-8 t <br /> Evaluation of parameters at MW-8 will be focused on parameters that have previously exceeded the <br /> Regulation 41- Colorado Basic Standards for Groundwater(5 CCR 1002, BSGW) at the existing site wells ' <br /> screened in the same formation—specifically MW-4, MW-6, and MW-7. These parameters include barium, iron, <br /> manganese, total dissolved solids (TDS), and chloride. <br /> To evaluate the results from MW-8, an approach has been developed to determine the comparability of the new ' <br /> samples with the existing water quality at MW-4, MW-6, and MW-7. Two methods will be used for determining the <br /> magnitude of difference between the samples: a visual/graphical comparison and a mathematical comparison. For <br /> the visual and graphical comparison, time series of the collected data will be updated and reviewed following each ' <br /> sampling event and box and whisker plots will be updated. <br /> For the mathematical approach, MW-8 will be assessed using a relative percent difference(RPD)method,treating the ' <br /> samples as though they are laboratory duplicates,to determine if they are likely to have been drawn from the same <br /> population. This approach was selected because it will allow for the comparison of individual data points rather than a <br /> larger minimum data set(i.e., more sampling events) utilized in other methods, in turn allowing for determination of ' <br /> differences on an expedited schedule. Since variability in concentrations is observed between sampling events,this <br /> comparison will be conducted for three sampling rounds once the water levels and data are stable. If at least one <br /> sampling round demonstrates the results are comparable, a demonstration can be made that the concentrations ' <br /> observed in MW-4, MW-6, and MW-7 are reflective of background (i.e., similar to MW-8). <br /> RPD values will be calculated when both the MW-8 results and the mean of the recent results from MW-4, MW-6, ' <br /> and MW-7 were greater than 5 times the practical quantitation limit (PQL; USEPA 2017). RPDs are calculated <br /> according to the following formula: <br /> %RPD = I A +B A —BI x 200 ' <br /> Where: A is the concentration of the applicable result at MW-8; and <br /> B is the corresponding concentration mean of recent data at MW-4, MW-6, and MW-7. <br /> GOLDER 4 ' <br />