2014-08-27_GENERAL DOCUMENTS - M1977348

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Colorado Division of Mining Reclamation and Safety August 22, 2014 Eric Scott 2 1400159 basins straddle the Wyoming /Colorado border and are approximately 80 miles west and northwest of the site. The Niobrara Formation occurs as part of the Cody shale unit of the Washakie and Sand Wash basins. Five groundwater chemistry samples of produced water were collected from production well heads from the Niobrara Formation. The samples had concentrations of barium between 0.19 and 42 milligrams per liter (mg /L), with an average concentration of 15.5 mg /L. TDS concentrations in these samples ranged between 2,270 mg /L and 45,600 mg /L, with an average concentration of 22,200 mg /L. These findings indicate that elevated barium and TDS concentrations are naturally occurring in Niobrara aquifer groundwater. Li (2013) characterized produced water quality within the Wattenberg Field in Colorado from wells screened along the interface of the Niobrara Formation and the Codell Sandstone, and solely in the Codell. For the tested production waters across 66 wells, the average TDS was 18,285 mg /L and the average barium concentration was 18.2 mg /L. Li attributes the presence of barium within the formation water to the surrounding limestone and shale, noting average whole rock barium concentrations of 10 milligrams per kilogram (mg /kg) and 580 mg /kg, respectively. Barium Occurrence in Bedrock 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 t 28.04 mg /kg and 503.87 t 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 i \14\ 1400159\ 0122\ tm- banumconcentrations_fnl- 22aug14 \1400159 tm- banumconcentrations_fnl- 22aug14 docx - Associates