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2018 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 2018 and similar to previously reported values by RGI (1999) and previous <br /> groundwater monitoring reports for this site. <br /> ' 3.2 Analytical Results <br /> Laboratory analyses of the 2018 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 2018). <br /> Concentrations of metals and other constituents measured in groundwater at well MW-7 were compared <br /> 1 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). None of the parameters exceeded their <br /> NPLs by more than 10 percent. Therefore, pursuant to the DRMS (2009) GMP approval letter, sampling <br /> of MW-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 /> - . , 6 <br />