2019-07-23_REVISION - M1977348 - Laserfiche WebLink

Home Browse Search

July 19,2019 18107649 ■ Chloride: Chloride concentrations are greater in the Group 3 versus Group 2 wells. Exceedances of the interim narrative standard have consistently occurred in the Group 2 and Group 3 wells. In the Group 3 wells chloride concentrations generally showed increasing trends in the initial sampling events for each well. Concentrations of chloride in SPLP leachate are less than one order of magnitude greater for CKD samples than for samples of native materials. Sulfate: In some of the Group 3 wells(MW-4 and MW-7)sulfate concentrations initially exceed the interim narrative standard but concentrations generally decreased after the initial sampling events for each well. Exceedances of the interim narrative standard have consistently occurred in the Group 1 wells. 1 Concentrations of sulfate in SPLP leachate are approximately one to two orders of magnitude greater for CKD samples than for samples of native materials. 9 Fluoride: Fluoride concentrations are the highest in well MW-3. Fluoride concentrations consistently I exceeded the interim narrative standard at well MW-3, but only one sample has exceeded the standard in other site wells. This sample was collected in May 2010 from well MW-4. Fluoride was not monitored from 2015-2017. Concentrations of boron in SPLP leachate are approximately one order of magnitude greater for CKD samples than for samples of native materials. 61, TDS: TDS concentrations are greater in the Group 3 versus Group 2 wells. TDS concentrations are consistently greater than the 10,000 mg/L Standard have consistently occurred in the Group 1, Group 2, and Group 3 wells. In the Group 2 and Group 3 wells manganese concentrations were generally higher in the earlier sampling for each well and decreased with time. TDS concentrations in SPLP leachate are approximately one to two orders of magnitude greater for CKD samples than for samples of native materials. • Laboratory and Field pH: In Group 2 wells, there have been a handful of laboratory of field pH exceedances ' of the interim narrative standard for pH, the most recent occurred in June 2011. The SPLP leachate pH values are greater than 12 for the CKD material and between 7 and 10 for the native materials • Gross Alpha: Gross alpha has been consistently reported at low or negative concentrations with large uncertainty(e.g., -33±18 picocuries per liter(pCi/L))and varies widely within each well and between wells Gross Alpha was not measured in SPLP leachates. 1 With the exception of boron and fluoride, the highest concentrations of constituents that exceed the interim narrative standard in downgradient wells are found in samples collected from the Group 3 wells(MW-4, MW-6 and MW-7). These wells are located more than 500 feet downgradient from CKD disposal area A2. Group 2 wells (MW-2 and MW-3)are located less than 100 feet downgradient from the CKD disposal area A2 and have lower observed concentrations. This downgradient increase in concentrations suggests that the elevated concentrations reflect the influence of native host materials rather than influence from CKD leachate(from area A2). If the CKD deposited in area A2 was an ongoing source of loading to the groundwater, higher concentrations would be expected closer to CKD disposal area A2 in the Group 2 wells. This is particularly the case given that MW-2 and MW-3 are screened across the Niobrara/Codell contact where groundwater would be expected to flow based on the understanding of Site hydrogeology(Secor 1998, Golder 2013, Golder 2014). Although concentrations of some constituents in MW-4 increased in the 1998 and 1999 samples, the concentrations have been stable since groundwater sampling resumed in 2010. This suggests that current concentrations are more typical of formation concentrations and no significant trends are occurring. �, G ®LDER 7