2015-02-17_HYDROLOGY - M1977348 - Laserfiche WebLink

Home Browse Search

Colorado Division of Mining Reclamation and Safety February 17, 2015 Eric Scott 2 1400159 Group 1 (MW -1 and MW -5): The monitoring wells in Group 1 have screened intervals that are located less than 70 feet below ground surface (ft bgs) and are the furthest west and north of the Site wells. MW -1 is screened across the Niobrara /Codell contact near CKD area A2 and MW -5 is screened in the overburden above bedrock north of the CKD disposal areas. The pH of samples collected from these wells ranges between 7.3 and 8.2. The groundwater in this group is sodium - sulfate type water, as shown by the Piper diagram on Figure 2, with TDS concentrations between 6,020 and 7,800 milligrams per liter (mg /L), which is generally lower than the other groups. The groundwater in this group exhibits higher concentrations of calcium, magnesium, and sulfate and lower alkalinity than the other groups. Barium concentrations in this group are below 1 mg /L, which is lower than that of the other groups. Group 2 (MW -2 and MW -3): The monitoring wells in Group 2 are screened from approximately 100 to 200 ft bgs across the Niobrara /Codell contact. The wells in this group are located less than 100 feet downgradient to the east of CKD disposal area A2. The groundwater in this group is sodium - chloride type water (Figure 2) with TDS concentrations between 5,000 and 10,000 mg /L. The pH of samples collected from these wells ranges between 7.9 and 8.9. The groundwater in this group of wells exhibits higher alkalinity concentrations than that of the other groups and barium concentrations in this group are between 1 and 2 mg /L. Group 3 (MW-4, MW -6 and MW -7): Monitoring wells in Group 3 are screened at depths greater than 180 ft bgs, in the Niobrara Formation above the Niobrara /Codell contact'. The wells in this group are located greater than 500 feet downgradient or side - gradient to CKD disposal area A2. The pH of samples collected from these wells ranges between 7.6 and 8.3. The groundwater in this group is sodium - chloride type water with TDS concentrations that are greater than 10,000 mg /L. The signatures for groundwater from these three wells plot closely together on a piper diagram (Figure 2) as the groundwater in this group exhibits higher sodium and chloride concentrations than the other groups. Barium concentrations in this group are above 2 mg /L, which are higher than those of the other groups. Results from groundwater samples collected from the Group 3 wells indicate that constituent concentrations have taken longer to reach equilibrium with the surrounding formations than those for the wells in the other groups. For example, concentrations of chloride and sodium (both relatively conservative constituents) in MW -6 and MW -7 increased following installation of the wells and within approximately one year of well installation reached relatively stable concentrations similar to those in MW- 4 (Figure A -7 and Figure A -12, respectively). A similar trend was observed for MW -4 following installation ' Screened lithology of MW -4 is unknown. MW4 is assumed for this discussion to be part of Group 3 based on the well depth, hydraulic characteristics and chemical signature. 2 Conservative constituents are relatively unreactive and their concentrations are not expected to be changed by geochemical processes such as mineral precipitation and /or sorption along a flow path. Therefore their concentrations are relatively conservative along a flow path. -�'_If Golder is \14\ 1400159 \0100 \0122 \tm- boettchedimestone ua fnl- 17feb15 \1400159 tm- boettcherlimestone ua fnl- 17feb15.docx Associates 9 RY_ Q RY_