Laserfiche WebLink
April 2014 23 10381640A <br />• What is the current extent of the impacted groundwater and can it be shown that the <br />impact is still confined to within the permitted area? <br />• What is the local geology and how might Site geology influence future migration of <br />impacted groundwater? <br />• How does local geology relate to the construction of the Site monitoring wells and nearest <br />surrounding /downgradient wells? <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 />• 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 />• What steps should be taken to minimize the current and future impact(s) to Site <br />groundwater (source removal /isolation, treatment, etc.)? <br />• Additional appropriate monitoring and compliance well(s) will need to be installed for <br />future groundwater monitoring. <br />Based on the groundwater characterization information detailed herein, responses to these questions are <br />provided below: <br />"What is the current extent of the impacted groundwater and can it be shown that the impact is <br />still confined to within the permitted area "? <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 disposal in area A2. <br />Furthermore, groundwater has traveled approximately 40 feet through the bedrock since CKD <br />material was first placed in the disposal area A2. The distance from the eastern limits of the CKD <br />disposal area A2 to the Site's eastern permit boundary is approximately 1,260 feet. Based on the <br />conservative groundwater transport assumptions described above, CKD leachate migration to the <br />eastern permit boundary would require more than 450 years, even without accounting for <br />constituent sorption by bedrock materials. <br />"What specifically is the local geology? How might Site geology influence future migration of <br />impacted groundwater "? <br />The Site hydrogeology is described in Section 2.5 of this Report. In summary, alternating bands <br />of limestone, argillaceous limestone and shale form the Niobrara Formation which sits on top of <br />the Codell Sandstone. The formations dip at approximately 16 degrees in a general easterly <br />direction, and groundwater is thought to migrate along this contact. The general groundwater flow <br />direction is from west to east (Figure 1). The formations are characterized by low hydraulic <br />conductivity values and a conservatively estimated groundwater velocity of 7.9 x 10-3 ft/day, <br />Golder <br />i:NO \81640a\ 0400\ gwcharwellinstallfiNdrap _fnl- 30apr14 \10381840a gwcharrpt_holcim- bcettcher _ fnl- 28aprt4- with holdm edits.docx <br />Associates <br />