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2022 Groundwater Monitoring Report <br />www.arcadis.com <br />2022 Holcim FINAL GWMR 05132022 6 <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 contours <br />(Figure 2). The water table is encountered in the Codell Sandstone Member of the Carlile Formation (RGI 1999), <br />which underlies the quarried rock. All of the monitoring wells are screened in the Codell Sandstone. The <br />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 zone in <br />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 Sandstone <br />hydraulic conductivity of approximately 4.5 x 10-6 centimeters per second (RGI 1999), and a range of effective <br />porosities for sandstone of 5 to 30 percent (Freeze and Cherry 1979), the resulting groundwater velocity is 0.33 <br />foot to 1.99 feet per year. The resulting groundwater velocity, when including wells NP-1 and DP-1 in the average <br />hydraulic gradient calculation, is 0.36 foot to 2.19 feet per year. The range in 2022 was similar to previously <br />reported values by RGI (1999) and previous groundwater monitoring reports for this site. <br />3.2 Analytical Results <br />Laboratory analyses of the 2022 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 groundwater quality <br />data are provided in Appendix E (updated with results through 2022). <br />Concentrations of metals and other constituents measured in groundwater at well MW-7 were compared to the <br />NPLs approved by the DRMS in February 2009 and the potassium to sodium ratio NPL (0.5) approved by the <br />DRMS in February 2015 (see Section 1.3.5). The concentration of total iron exceeded the approved NPL by more <br />than 10 percent. However, no other exceedances were observed. Therefore, pursuant to the DRMS (2009) GMP <br />approval letter, resampling of MW-7 is not required. Sampling 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 well) were <br />sampled as part of the annual groundwater monitoring program. Analytical results are 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 27, 2012 <br />(Appendix A). All analytes measured in MW-13 were below their respective NPLs except for sulfate. However, <br />sulfate concentrations did not exceed the NPL by more than 10 percent and therefore, monitoring frequency will <br />remain on an annual schedule per the DRMS (2012) NPL determination letter. <br />Time series graphs of the potassium to sodium ratio, TDS, sulfate, manganese, total iron and TSS, 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 potential <br />impacts of CKD disposal to the groundwater. <br />In general, the following trends area observed: