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April 2014 24 10381640A <br />meaning groundwater travels one foot through the rock formations in approximately 130 days. <br />Secor (1998) indicated that the native materials found beneath the Site attenuate barium, lead <br />and thallium found in the CKD SPLP leachate, thus suggesting that these metals are moving <br />slower than infiltrating groundwater. Furthermore, concentrations of barium and TDS observed in <br />the Site monitoring well samples can be attributed to the local geology and likely do not represent <br />influence from CKD leachate disposal in area A2. <br />"How does local geology relate to the construction of the Site monitoring wells and nearest <br />surrounding /downgradient wells "? <br />With the exception of MW -5, groundwater was encountered at the Niobrara /Codell contact and <br />the Site wells were screened either just above or across this contact. Monitoring well MW -5 is <br />located side - gradient to the north of CKD disposal area A2 and is screened across the soil <br />overburden. Although lithology information is not available for the permitted downgradient water <br />supply wells, the water supply well depths downgradient of the Site are not great enough to <br />intercept the Niobrara /Codell contact. <br />"How does the current extent of impacted groundwater and Site geology compare to the <br />construction of surrounding wells? What is the likelihood that other nearby wells may be <br />impacted? Are nearby wells in the same aquifer "? <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. Additionally, review of <br />well permits near the Boettcher Quarry illustrated there are no permitted water supply wells within <br />a half mile downgradient of CKD disposal area A2 and screened in the same formation as the <br />Site wells. Due to the low hydraulic conductivity of the formations beneath the Site, it is highly <br />unlikely that water supply wells further than a half mile from CKD disposal area A2 would be <br />influenced by CKD leachate. Based on the conservative groundwater transport assumptions <br />described above, CKD leachate migration to the eastern permit boundary would require more <br />than 450 years, even without accounting for constituent sorption by bedrock materials. <br />"is there a well that is currently representative of "background conditions in the same <br />formation(s) that are now showing evidence of impact "? <br />No known upgradient or side - gradient water supply wells are installed in the same formation as <br />downgradient Site wells MW -2, MW -3, MW -4, MW -6 and MW -7. Furthermore, concentrations of <br />barium and TDS observed in the Site monitoring well samples are attributed to the local geology <br />and likely do not represent influence from CKD leachate disposal in area A2. <br />Golder <br />i \10 \81640a\ 0400 \gwcharwellinstall(ieltlrep_fnl 30apri4 \10387840a gwcharrpt_holcim boettcher_(nl 28apr14 vnth holcim edits.tlocx <br />Associates <br />