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2019 GROUNDWATER MONITORING REPORT <br /> 3 RESULTS <br /> 3.1 Groundwater Elevations and Flow Characteristics <br /> Measured depths to the groundwater surface(Table 1)were used to develop groundwater elevation <br /> contours (Figure 2). The water table is encountered in the Codell Sandstone Member of the Carlile <br /> Formation (RGI 1999), which underlies the quarried rock. All of the monitoring wells are screened in the <br /> ' Codell Sandstone. The groundwater flow pattern is similar to what has been observed in the past. <br /> Groundwater generally flows south toward the Arkansas River, which is the major groundwater discharge <br /> zone in the area, as reported by previous investigators (i e., BBL 2002; RGI 1999). <br /> Based upon an average measured horizontal groundwater gradient of 0.02 foot per foot, a Codell <br /> Sandstone hydraulic conductivity of approximately 4 5 x 10-6 centimeters per second (RGI 1999), and a <br /> range of effective porosities for sandstone of 5 to 30 percent (Freeze and Cherry 1979), the resulting <br /> groundwater velocity is 0.3 foot to 1 9 feet per year. The resulting groundwater velocity, when including <br /> wells NP-1 and DP-1 in the average hydraulic gradient calculation, is 0.3 foot to 2 feet per year. This <br /> range remained the same in 2019 and similar to previously reported values by RGI (1999) and previous <br /> 1 groundwater monitoring reports for this site. <br /> 3.2 Analytical Results <br /> 1 Laboratory analyses of the 2019 groundwater samples were conducted by ACZ. Results of the laboratory <br /> analyses are provided in Table 2. The laboratory report is provided as Appendix D. Historical <br /> groundwater quality data are provided in Appendix E (updated with results through 2019). <br /> Concentrations of metals and other constituents measured in groundwater at well MW-7 were compared <br /> to the NPLs approved by the DRMS in February 2009 and the potassium to sodium ratio NPL (0.5) <br /> approved by the DRMS in February 2015 (see Section 1 3.5). The concentration of total iron exceeded <br /> the approved NPL by more than 10 percent. However, no other exceedances were observed. Therefore, <br /> pursuant to the DRMS (2009) GMP approval letter, resampling of MW-7 is not required. Sampling of MW- <br /> 7 will remain on an annual schedule. <br /> In addition to MW-7, groundwater monitoring wells MW-12 (upgradient well)and MW-13 (compliance <br /> ' well) were sampled as part of the annual groundwater monitoring program. Analytical results are <br /> presented in Table 2. <br /> As discussed in Section 1.3.4 of this report, the DRMS set NPLs for MW-13 in a letter dated November <br /> 27, 2012 (Appendix A). All analytes measured in MW-13 were below their respective NPLs. <br /> Time series graphs of the potassium to sodium ratio, TDS, sulfate, manganese, total iron, and dissolved <br /> iron for MW-7, MW-12, and MW-13 were prepared (Figures 3,4, 5, 6, 7, and 8 respectively)to evaluate <br /> potential impacts of CKD disposal to the groundwater. <br /> In general, the following trends area observed: <br /> • Potassium to Sodium Ratio: As shown in Table 2 and on Figure 3, the potassium to sodium <br /> ratio in all monitoring wells continues to be generally less than 0.10, indicating that there is no <br /> ' arcadis com <br />