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July 19,2019 18107649 <br /> selenium, and thallium, and the majority of major ions. Upward trending concentrations would be expected if CKD <br /> was influencing groundwater concentrations in the Site wells. For example, potassium concentrations measured <br /> in the CKD leachate of approximately 500 mg/L are two orders of magnitude greater than that of the native <br /> materials. In contract, concentrations of potassium in groundwater from all wells are typically less than 20 mg/L, <br /> and show no consistent increasing trends in concentrations. <br /> 5.3 Sequential Batch Testing <br /> Secor performed sequential batch testing on the leachates produced by the SPLP tests as part of their 1998 <br /> hydrogeologic and geochemical assessment. The analytical methodology and results for the sequential batch <br /> testing are detailed in Secor(1998). The purpose of the sequential batch testing was to evaluate the attenuation <br /> capacity of the bedrock materials. The assessment looked at the behavior of arsenic, barium, chromium, lead, <br /> selenium and thallium. Secor reported that barium, lead and thallium from CKD leachate would sorb to the native <br /> materials and be attenuated along the groundwater flow path and that the particle velocity of these metals would <br /> be slower than groundwater velocity. The study was inconclusive for determining the sorption behavior for <br /> arsenic, chromium, and selenium. <br /> 6.0 RECLAMATION ACTIVITIES <br /> Reclamation activities at Site have primarily consisted of reseeding. The area where reseeding occurred is <br /> presented in Figure . <br /> 7.0 SUMMARY AND RECOMMENDATIONS <br /> Site groundwater characterization data support the conclusion that groundwater sampled from downgradient wells <br /> represents predominantly pre-1952 water, and at the time of and prior to tritium dating conducted in August 2014, <br /> represent ambient concentration. pre-January 31, 1994 groundwater. Based on these findings, Golder <br /> recommends: <br /> a recent data be used to assess ambient conditions as of January 30, 1994 <br /> a in cases where ambient conditions are greater than the Regulation 41 Table Values Standards, a less <br /> restrictive standard based on the ambient conditions can be applied. <br /> 1 Additionally, the following observations support the conclusion that concentrations observed in the downgradient <br /> Site groundwater monitoring well samples are attributed to local geology, and do not represent influence from CKD <br /> disposal in area A2. <br /> 1) Naturally occurring barium and TDS background concentrations are regionally elevated in the Niobrara <br /> aquifer groundwater, providing a likely explanation for elevated values of those analytes that is not related to <br /> CKD. <br /> 2) If CKD in area A2 was an ongoing source for loading to the groundwater, higher concentrations would be <br /> expected in the Group 2 wells that are closer to CKD disposal area A2, however the data indicate the <br /> opposite. The highest concentrations of most constituents are in groundwater samples from the Group 3 <br /> 1 wells(MW-4, MW-6 and MW-7), which are located greater than 500 feet from CKD disposal area A2. <br /> Group 2 wells (MW-2 and MW-3)are located less than 100 feet from the CKD disposal area and have lower <br /> concentrations of most constituents. <br /> GOLDER 12 <br />