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2017 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 2017 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 2017 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 2017). <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 /> recently approved by the DRMS(see Section 1.3.5). The concentration of total iron exceeded the <br /> 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, and manganese for MW-7, MW-12, <br /> and MW-13 were prepared (Figures 3,4, 5, and 6, respectively)to evaluate potential impacts of CKD <br /> disposal to the groundwater. <br /> In general, the graphs indicate that manganese concentrations in MW-7, MW-12, and MW-13 have <br /> continued to decrease through time. The graphs also indicate that TDS and sulfate concentrations in MW- <br /> 7 are generally decreasing through time. The concentrations of TDS and sulfate are generally stable in <br /> MW-12 and MW-13. The concentrations of analytes found in monitoring well MW-12,which is considered <br /> arcadis.com 6 <br />