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July 19,2019 18107649 <br /> 82 wells from within a mile of the southern portion of permit boundary, 62 of these wells where within a mile of <br /> disposal area A2 (Figure 6 and Table 10). The DWR search results has limited information on well screened <br /> intervals, water levels and general lithology. The majority of the well permits in the DWR database are west of the <br /> CKD disposal area. Based on the dip of the lithological units at the Site, only those wells that are located to the <br /> east of the CKD disposal area A2 have the potential to be screened across or immediately above the <br /> Niobrara/Codell contact. However, the screened interval of these wells(when known) is not deep enough to <br /> intercept the Niobrara/Codell contact, so water quality samples collected from them would not be relevant to <br /> evaluating the effect of the CKD disposal area A2 on groundwater quality. <br /> 3.3 Background Geochemical Conditions <br /> There is not a Site groundwater monitoring well located outside the areas of CKD disposal screened similarly to <br /> the downgradient Site wells. Therefore, a literature search was conducted to characterize naturally occurring <br /> 1 barium and total dissolved solids(TDS)concentrations in groundwater. In Colorado the Niobrara Formation and <br /> its surrounding formations are not generally considered good sources of groundwater, due to their low production <br /> rates (Pearl 1974). Consequently, information regarding groundwater quality is sparse for the Niobrara in <br /> Colorado. <br /> The Wyoming State Geological Survey published the Green River Basin Water Plan II, Groundwater Study in <br /> 2010(Surdam 2010). This study assessed groundwater resources in the Greater Green River Basin (GGRB)of <br /> southwestern Wyoming and adjacent areas in Colorado and Utah. This study divided the GGRB basin into sub- <br /> basins and characterized the aquifers' groundwater chemistry characteristics for water quality purposes. Two of <br /> the sub-basins identified are the Washakie and Sand Wash basins. These basins straddle the Wyoming/Colorado <br /> border and are approximately 80 miles west and northwest of the Site. The Niobrara Formation occurs as part of <br /> the Cody shale unit of the Washakie and Sand Wash basins. Five groundwater chemistry samples of produced <br /> water were collected from production well heads from the Niobrara Formation. The samples had concentrations of <br /> barium between 0.19 and 42 milligrams per liter(mg/L), with an average concentration of 15.5 mg/L. TDS <br /> concentrations in these samples ranged between 2,270 mg/L and 45,600 mg/L, with an average concentration of <br /> ' 22,200 mg/L. These findings indicate that elevated barium and TDS concentrations are naturally occurring in <br /> Niobrara aquifer groundwater. <br /> Li (2013)characterized produced water quality within the Wattenberg Field in Colorado from wells screened along <br /> the interface of the Niobrara Formation and the Codell Sandstone, and solely in the Codell. For the tested <br /> production waters across 66 wells, the average TDS concentration was 18,285 mg/L and the average barium <br /> concentration was 18.2 mg/L. Li attributes the presence of barium within the formation water to the surrounding <br /> limestone and shale, noting average whole rock barium concentrations of 10 mg/kg and 580 mg/kg for shale and <br /> limestone, respectively. <br /> 4.0 GROUNDWATER MONITORING RESULTS <br /> 4.1 Routine Sampling <br /> Water quality sampling results for Site wells are presented in Table 2 through Table 8. The analyte list has varied <br /> over the monitoring history; time series graphs through 2018 for routinely monitored constituents are presented in <br /> Appendix D. Based on lithology and depth of the wells, groundwater beneath the Site can be classified into three <br /> distinct groups(Figure 7). <br /> ,� GOLDEP 4 <br />