2019-03-05_REVISION - M1977348 (5)

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r March 1,2019 18107649 ' ■ Fall 2012: Installation of MW-5 through MW-7 , ■ 2013-2016: Quarterly sampling of MW-1 through MW-7 ■ 2017- Present: Semi-annual sampling of MW-1 through MW-7 ' 3.0 HYDROGEOLOGIC CONDITIONS 3.1 Geology ' The Boettcher Quarry was mined for Niobrara Formation limestone, which is of Cretaceous age and marine origin. The Niobrara Formation consists of alternating bands of limestone, argillaceous (i.e., clayey) limestone, and , calcareous shale (Ideal 1977). The argillaceous limestone bands are typically fossiliferous and contain trace amounts of pyrite. The Niobrara Formation is bounded by the older Codell sandstone (of the Carlile Formation) and the younger Pierre shale (Ideal 1962). The Niobrara Formation limestone is subdivided into members ' (bands), identified as A through G from older to younger aged rock. The E-band is further subdivided into bands E1 through E3 based on calcium oxide (CaO)content. The boundaries within the E-band are gradational, rather than discrete, based on physical or chemical characteristics (Ideal 1977). The A band was mined at the Site ' because of its high limestone grade. The A through G band names and approximate thicknesses are provided on Figure 2:. The Niobrara Formation strikes north-south and dips approximately 16 degrees to the east(Ideal 1977). The ' A-band forms a prominent north-south trending ridge or hogback along the west side of the Site and each of the overlying limestone bands form less prominent north-south hogbacks paralleling the A-band outcrop. These ' ridges are not present where the high lime content bands have been quarried. Changes in strike represent zones of flexure and are seen as a bend or curve in the hogback. There are some minor changes in dip and minor faulting (with small displacements)within these flexure areas (Ideal 1977). Such a curve/band is located in CKD ' disposal area A2. Figure 3 provides a generalized cross section through CKD disposal area A2. Barite-rich nodules were identified within the Niobrara Formation at a site in Fairburn, South Dakota (Tourtelot and Cobban 1968). Within the nodules, barite was noted as a replacement for organic constituents within a ' surrounding matrix of carbonate. Barite mineralization was not found within the deposit outside of the nodules, or in other nodules identified within the Niobrara by Johnson (1930) near Pueblo, Colorado. Outside the context of nodule formation, multiple authors have noted the presence of barium as a significant trace ' metal within various portions of the Niobrara and associated formations. Kulp and Pratt(2004)found a range of barium concentrations in samples from South Dakota and Wyoming of Smoky Hill Chalk (an end-member of the ' Niobrara Formation) and Pierre Shale (the formation overlying the Niobrara)of 11.45 ± 28.04 milligrams per kilogram (mg/kg)and 503.87 ±237.38 mg/kg, respectively. Arthur et al. (1985)found regional barium maxima above 1,000 mg/kg in the Bridge Creek Limestone near Pueblo, CO, and above 2,500 mg/kg within the Fort Hays and Smoky Hill Members of the Niobrara as sampled at the former Ideal Cement Quarry Site near Fort Collins — now known as the Boettcher Quarry. Arthur et al. (1985) noted that the highest barium concentrations identified 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). ;, GOLDER 2