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July 19,2019 18107649 within the Niobrara Formation are thought to occur in oxidized zones directly adjacent to strata with increased organic carbon contents. Other representative examples of barium concentrations within the Niobrara and associated surrounding formations can be found in Dean and Arthur(1998)and Landis(1959). 3.2 Hydrogeology The Site is located in the Colorado Piedmont subprovince. The Dakota-Cheyenne aquifer is the principal aquifer of the Colorado Piedmont subprovince, and is comprised of the Early Cretaceous Dakota Sandstone and the Cheyenne Sandstone Member of the Purgatoire Formation (Topper and others 2003), and is overlain by the Carlile Formation and Niobrara Formation (Figure 3). The Niobrara Formation and Carlile Formation are not considered to be part of a principal aquifer system, but portions of these units can yield some water to a few stock wells in parts of the Colorado Piedmont(Topper and others 2003). The Niobrara formation is described by the Colorado Geological Survey as a fractured limestone that locally may yield small amounts of poor quality water (Pearl 1974). Previous mining activities and the existing monitoring wells at the Site are limited to the Niobrara Formation and the top of the Carlile Formation (the Codell sandstone), and do not penetrate into the Dakota- Cheyenne aquifer. jGroundwater at the Site has been thought to occur along the contact of the Codell sandstone and the Fort Hayes limestone(A band) members(Secor 1998). While fractures are noted in borehole logs and previous hydraulic studies, the joint structure is unknown and does not appear to be continuous(SEC 1990). An approximately 20- foot thick sandstone interval at the top of the Codell Sandstone is thought to be the only significant groundwater flow unit near the CKD disposal area (DRMS 2014). The groundwater flow direction has been observed to generally flow easterly. Hydraulic testing was performed on six of the monitoring wells at the Site. Hydraulic rising and falling head slug tests were performed on MW-1, MW-2, MW-3, MW-4 and MW-5(Secor 1998, Golder 2010 and Golder 2012). Hydraulic packer injection testing was performed during the advancement of borehole MW-7 (Golder 2013). Hydraulic testing results are summarized in Table 9. Figure 4 presents a graph of the monitoring well water elevations measured during each sampling. Wells MW-1 1 and MW-5 exhibit minimal drawdown during sampling and are relatively stable through time, indicating little seasonal influence on groundwater elevation. Historical (1999-2000)water level measurements in MW-2 and MW-4 slowly increased with time, indicating that the water levels in these wells had not stabilized and may not have been in equilibrium with the surrounding formation at the time of this sampling. The water level recorded when monitoring resumed in 2010(prior to well redevelopment), were higher than the historical measurements and may have reflected recovery to static conditions. Once quarterly monitoring began in 2011, the water levels in MW-2 and MW-4 decreased further. Since changing to semi-annual sampling in 2017, water levels have been stable in MW-3. However, water levels in MW-2, MW-4, MW-6, and MW-7 showed an increase following the change to semi-annual sampling indicating increased recharge between sampling events. The variations in water level elevation over time for wells MW-2, MW-3, MW-4, and MW-6, and MW-7 from 2011 through 2018 correlate with the number of days elapsed between sampling events i.e. the amount of recharge observed in these well increases with time elapsed (Figure 5). This pattern of slow and time dependent recharge is consistent with the observations related to groundwater age discussed below. Additionally, these patterns in water level support the observation that many of the site wells took an extended period of time to reach equilibrium with the surrounding formations and early data (both hydrogeologic and chemical)was likely not representative of actual formation conditions. A review of the well permits near the Boettcher Quarry included a search of the Colorado Division of Water Resources (DWR)online database for information on local well permits. This review resulted in permits for ,> GOLDER 3