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July 19,2019 18107649 <br /> i <br /> SPLP leachate of the CKD materials is calcium-sulfate dominant and plots in a different region of a piper diagram <br /> than water from the down gradient wells (Figure 8). If the CKD was a source of elevated concentrations, you <br /> would expect sulfate and calcium to Increase, and groundwater samples In the piper diagram would migrate away <br /> from the sodium-chloride water type that is currently noted. However;following installation, concentrations of <br /> sulfate and calcium in Group 3 wells decreased,while concentrations of chloride increased, suggesting no mixing <br /> with CKD leachate. <br /> 4.3 Groundwater Age Dating <br /> To assess the recharge age for the water monitored in the Site wells relative to CKD disposal, groundwater <br /> samples were collected on August 27, 2014 for tritium analysis from all of the Site wells except MW-5. Well MW-5 <br /> was not tested for tritium because of its proximity to a non-backfilled pit at the Site which likely acts as a localized <br /> recharge zone. Field sheets associated with the tritium sampling event are presented in Appendix E. Tritium <br /> sampling was conducted during a routinely schedule sampling event following the sampling procedures outlined in <br /> the sampling and analysis plan for the site (Golder 2010). Wells MW-3, MW-4, MW-6 and MW-7 were purged dry <br /> on August 18, 2017; and more than three casing volumes were purged from well MW-1 on the day of sampling. <br /> Well M-2 was not able to be purge to complete dryness due to a bailer malfunction. Purging and sampling was <br /> conducted with a disposable bailer for all wells except for MW-3, which was sampled with an inertial pump. <br /> Samples for the tritium analysis were placed in dry 500 mL plastic bottles. Samples were shipped securely in a <br /> ' cooler(without ice). <br /> Laboratory analysis for tritium was conducted by the Environmental Isotope Laboratory at the University of <br /> Arizona. Other sources of radiation present in a water sample(uranium, gross alpha, gross beta)do not influence <br /> the tritium measurements (Eastoe 2019) The laboratory results are presented in Appendix F. Appendix F <br /> includes results for"MW-20,"which was a blind duplicate for MW-6 submitted to the laboratory. <br /> Tritium (3H) is the radiogenic isotope of hydrogen and decays with a half-life of 12.23 years to helium (3He). <br /> Tritium concentrations are measured in tritium units(TU), where 1 TU is equal to 1 tritium atom per 1018 hydrogen <br /> atoms. Although small amounts of tritium occur naturally through cosmic ray interactions with atmospheric gases, <br /> tritium was introduced to the environment in significant concentrations through nuclear weapons testing, which <br /> began in 1952. Tritium concentrations in precipitation prior to weapons testing are not well known but likely did not <br /> exceed 2 to 8 TU (Rupert and Plummer, 2004). Therefore, due to tritium decay, pre-1952 waters would currently <br /> have tritium concentrations near 0.4 TU (less than the 0.6 TU detection limit used in this study). <br /> Tritium concentrations in the atmosphere peaked in 1963 (Clark and Fritz, 1997). Since 1963, tritium <br /> concentrations in precipitation have decreased because of the discontinuation of weapons testing, exchange of <br /> water with the oceans, and the short half-life of tritium. Clark and Fritz(1997) presented a qualitative interpretation <br /> of tritium levels for continental regions(Table 11)as of 1997. <br /> The tritium value for modern (or current) precipitation and recharge is affected by many factors. The factors <br /> include time, coastal proximity, seasonal variation and latitude. The time has affected levels of tritium in <br /> precipitation due to isotope decay and exchange of waters within the hydrologic cycle. The exchange of waters is <br /> more prevalent in coastal regions, so the levels of tritium in precipitation are lower near the oceans. Tritium <br /> concentrations in precipitation typically have strong seasonal variations; therefore, estimates of tritium in <br /> precipitation typically are not based on any one storm event but are often aggregate-based to account for <br /> seasonal and individual storm variation, all of which would contribute to groundwater tritium levels. <br /> GOLDER 8 <br />