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' March 1,2019 18107649 <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 CKD-INFLUENCED GROUNDWATER COMPARISONS <br /> For reference and comparison, CKD-influenced groundwater samples were collected and analyzed at another, out <br /> ' of state Holcim site. Compared to the Boettcher Quarry, the groundwater from the comparison site exhibits a high <br /> pH of 12.6, high alkalinity of 2,120 mg/L as CaCO3, present as hydroxide alkalinity, a TDS concentration of <br /> 2,840 mg/L, and lower(<50 mg/L) concentrations of chloride and sulfate. The groundwater at this comparison <br /> ' site has an elevated potassium concentration of 797 mg/L, but a low total barium concentration of 0.35 mg/L. The <br /> high pH and elevated potassium concentration are characteristic of CKD influences on groundwater, consistent <br /> with the SPLP testing results. However, elevated pH or levels of these constituents are not present in the <br /> Boettcher Quarry groundwater samples. In addition, the relatively high chloride, sulfate and barium concentrations <br /> observed in the Boettcher Quarry Group 3 wells are not observed in the comparison site CKD-impacted <br /> groundwater, indicating the relatively high chloride, sulfate, and barium are representative of local groundwater. <br /> ' The major ion differences between Site groundwater and the comparison site are highlighted in Figure 5, in which <br /> the potassium-hydroxide CKD influenced water plots on the opposite side of the diagram than the sodium-sulfide <br /> and sodium-chloride Site waters. Similarly, the SPLP results for CKD samples collected at the Site plot closer to <br /> the CKD influenced water than Site groundwater. <br /> 7.0 RECLAMATION ACTIVITIES <br /> Reclamation activities at Site have been intended to help protect existing and potential future uses of <br /> groundwater, and have primarily consisted of reseeding. The area where reseeding occurred is presented in <br /> ' Figure 11. <br /> 8.0 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 concentrations pre-January 31, 1994 groundwater. Based on these findings, Golder <br /> ' recommends that the recent data be used to assess ambient conditions as of January 30, 1994; and 2) in cases <br /> where ambient conditions are greater than the Regulation 41 Table Values Standards, a less restrictive standard <br /> based on the ambient conditions be applied. <br /> ' Findings from the tritium groundwater dating program,which indicate that groundwater sampled in MW-1 recharged <br /> relatively recently and that tritium levels for groundwater in the other Site wells represent predominantly pre-1952 <br /> ' water, are consistent with other groundwater characterization observations for the Site. The following observations <br /> support the conclusion that concentrations of barium and TDS observed in the Site groundwater monitoring well <br /> samples are attributed to local geology, and do not represent influence from CKD 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 /> ' J GOLDER 9 <br />