Laserfiche WebLink
April 2014 25 10381640A <br />"What steps should be taken to minimize the current and future impact(s) to Site groundwater <br />(source removal isolation, treatment, etc.) "? <br />Concentrations of barium and TDS observed in the Site monitoring well samples are attributed to <br />the local geology and likely do not represent influence from CKD leachate; therefore, groundwater <br />impact mitigation is not appropriate at this time. <br />"Suggested additional appropriate monitoring and compliance wells) to be installed for future <br />groundwater monitoring "? <br />Groundwater monitoring wells MW -5, MW -6 and MW -7 were installed in December 2012 in <br />response to this comment. <br />5.1.4 Conclusions and Recommendations <br />Site groundwater characterization data support the conclusion that concentrations of barium and TDS <br />observed in the Site groundwater monitoring well samples are attributed to local geology, and do not <br />represent influence from CKD leachate disposal in area A2. This conclusion is based on the following <br />observations. <br />1. The highest barium and TDS concentrations are in groundwater samples from the <br />Group 3 wells (MW -4, MW -6 and MW -7), which are located greater than 500 feet from <br />CKD disposal area A2. <br />2. Group 2 wells (MW -2 and MW -3) are located less than 100 feet from the CKD disposal <br />area and have lower concentrations of barium and TDS. <br />3. If CKD in area A2 was an ongoing source for barium and TDS loading to the <br />groundwater, higher concentrations would be expected closer to the CKD disposal area <br />A2. <br />4. SPLP leachate pH values are greater than 12 for the CKD material and between 7 and <br />10 for the native materials. Groundwater pH values at the Site are between 7 and 9, <br />which are similar to values observed in the wells prior to CKD placement in area A2, and <br />do not show an increase over time that would be expected if the waters were being <br />influenced by CKD leachate. <br />5. Dissolved metals concentrations elevated above benchmark levels are only consistently <br />observed for barium. Elevated or upward trending concentrations of other constituents <br />would be expected if CKD leachate was influencing groundwater concentrations in the <br />Site wells. <br />6. Naturally occurring barium and TDS background concentrations are regionally elevated in <br />the Niobrara aquifer groundwater. <br />7. It is conservatively estimated that groundwater has traveled approximately 40 feet <br />through the bedrock beneath the Site since CKD was first placed in disposal area A2. <br />Although groundwater that has come in contact with CKD from area A2 is possibly being <br />monitored in wells MW -3 and MW -2, it is unlikely that groundwater that has come into <br />Golder <br />i110 \81640a\ 0400 \gwehar llinslallfieldrep _fnl- 30aprl4\10381640a gwcharrpt _holcim- boettcher_fnl- 28apr14- with holcim edits docx GAssociates <br />