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Colorado Division of Mining Reclamation and Safety February 17, 2015 <br />Eric Scott 4 1400159 <br />alkalinity, TDS concentrations of 2,840 mg /L, and lower ( <50 mg /L) concentrations of chloride and sulfate. <br />The groundwater at this comparison site has an elevated potassium concentration of 797 mg /L, but a low <br />total barium concentration of 0.35 mg /L. The high pH and elevated potassium concentration are <br />characteristic of CKD influences on groundwater, consistent with the SPLP testing results. However, <br />elevated pH or levels of these constituents are not present in the Boettcher Quarry groundwater samples. <br />In addition, the relatively high chloride, sulfate and barium concentrations observed in the Boettcher <br />Quarry Group 3 wells are not observed in the comparison site CKD- impacted groundwater, indicating the <br />relatively high chloride, sulfate, and barium are representative of local groundwater. The major ion <br />differences between Site groundwater and the comparison site are highlighted in Figure 2, in which the <br />potassium- hydroxide CKD influenced water plots on the opposite side of the diagram than the sodium - <br />sulfide and sodium - chloride Site waters. Similarly, the SPLP results for CKD samples collected at the <br />Site plot closer to the CKD influenced water than Site groundwater. <br />3.0 HYDROGEOLOGIC CONDITIONS <br />The groundwater flow direction is generally from west to east across the Site. Figure 1 shows the <br />4th quarter 2013 monitoring well groundwater elevations and general groundwater flow direction. Due to <br />the low hydraulic conductivity that is typical of Site wells, it is possible that at least some of the measured <br />water levels do not represent true static conditions. <br />4.0 GROUNDWATER AGE <br />To assess the recharge age for the water monitored in the Site wells relative to CKD disposal, <br />groundwater samples were collected for tritium analysis from all of the Site wells except MW -5 on <br />August 27, 2014. Well MW -5 was not tested for tritium because of its proximity to a non- backfilled pit at <br />the Site which likely acts as a localized recharge zone. Laboratory analysis for tritium was conducted by <br />the Environmental Isotope Laboratory at the University of Arizona. The laboratory results are presented in <br />Attachment B. Appendix B includes results for "MW -20," which was a blind duplicate for MW -6 submitted <br />to the laboratory. <br />Tritium (3H) is the radiogenic isotope of hydrogen and decays with a half -life of 12.23 years to helium <br />(3 He). Tritium concentrations are measured in tritium units (TU), where 1 TU is equal to 1 tritium atom per <br />1018 hydrogen atoms. Although small amounts of tritium occur naturally through cosmic ray interactions <br />with atmospheric gases, tritium was introduced to the environment in significant concentrations through <br />nuclear weapons testing, which began in 1952. Tritium concentrations in precipitation prior to weapons <br />testing are not well known but likely did not exceed 2 to 8 TU (Rupert and Plummer, 2004). Therefore, <br />due to tritium decay, pre -1952 waters would currently have tritium concentrations near 0.4 TU (less than <br />the 0.6 TU detection limit used in this study). <br />,4 . <br />Golder <br />is \14\ 1400159 \0100 \0122 \tm- boettchedimeslone uar fnl- 17febl5 \1400159 tm- boettcherlimestone uar fnl- 17feb15.docx Associates <br />9 �Y_ Q rY_ <br />