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April 2014 14 10381640A <br />exception of MW -4 and MW -7. The majority of dissolved trace metals concentrations are in the range of <br />the other Site wells. <br />A number of constituent concentrations have not stabilized since the monitoring well was installed. <br />Dissolved manganese, calcium and potassium have been decreasing in concentration and dissolved <br />barium, sodium, chloride, TDS, and total alkalinity concentrations have been increasing since well <br />installation. The trends are similar to the trends observed in MW -4 for barium, chloride, TDS, and sulfate <br />between April 1999 and July 2000. These trending concentrations indicate that the well was likely not in <br />equilibrium with the surrounding formation and may not be reflective of groundwater conditions prior to <br />drilling. These trends may be the result of disturbance to the system created by drilling and well <br />installation. <br />4.1.7 Monitoring Well MW -7 <br />Monitoring well MW -7 is located hydraulically side - gradient of CKD disposal area A2. Benchmark analyte <br />levels were not determined for well MW -7. Groundwater samples collected from MW -7 are predominantly <br />sodium - chloride type waters (Figure 4). The samples exhibit similar major ion concentrations to wells MW -4 <br />and MW -6, and have higher chloride and sodium concentrations than the other Site wells. MW -7 samples <br />have pH values ranging from 7.9 to 8.1, with no trending of values since well installation. The TDS <br />concentrations are generally greater than the other Site wells with the exception of MW -4. The majority of <br />dissolved trace metals concentrations are in the range of the upgradient wells. A number of constituent <br />concentrations have not stabilized since the monitoring well was installed. Dissolved manganese, calcium <br />and potassium have been decreasing in concentration and dissolved barium, sodium, chloride, TDS, and <br />total alkalinity concentrations have been increasing since well installation. The trends are similar to the <br />trends observed in MW -4 for barium, chloride, TDS, and sulfate between April 1999 and July 2000. These <br />trending concentrations indicate that the well was likely not in equilibrium with the surrounding formation <br />and may not be reflective of groundwater conditions prior to drilling. These trends may be the result of <br />disturbance to the system created by drilling and well installation. <br />4.1.8 Other Observations <br />Groundwater beneath the Site can be classified into three distinct groups. These groups are distinguished <br />based on water chemistry, monitoring well screened intervals and aquifer lithology. The characteristics of <br />each group are discussed below. <br />Group 1 (MW -1 and MW -5): The monitoring wells in this group have screened intervals that are less than <br />70 feet below ground surface (ft bgs) and are the furthest west of the Site wells. MW -1 is screened across <br />the Niobrara /Codell contact and MW -5 is screened in the overburden above bedrock. The groundwater in <br />this group is sodium - sulfate type water with TDS concentrations between 6,020 and 7,800 mg /L, which is <br />Jam Golder <br />i:NO \81840a\ 0400 \gwcharwellinstallfieltlrep_fnl 30apr14 \10381640a gwchartpt_holcim bcet[cher_fnl 28apr14 with holcim edits.docx <br />Associates <br />