2014-05-05_HYDROLOGY - M1977348 - Laserfiche WebLink

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I April 2014 21 10381640A 5.0 SUMMARY AND RECOMMENDATIONS The purpose of the present study is to address the questions presented in the June 25, 2012 DRMS letter (DRMS 2012) and to evaluate an appropriate path forward to achieving full release of reclamation liability for the Site in accordance with Section 3.1.7 of the Construction Materials Rule. The DRMS questions addressed herein involve the nature and extent of groundwater impacts from the Site (if any), the influence of hydrogeological conditions on groundwater and constituent transport, and potential receptors hydraulically downgradient from the Site. The DRMS noted consistent benchmark exceedances of barium in groundwater concentrations at monitoring wells MW -3 and MW -4, consistent benchmark exceedances of TDS at MW -4, and minor benchmark exceedances of boron at MW -3. To address the DRMS questions and concerns about these constituent exceedances, we have evaluated if the observed concentrations of barium and TDS are from CKD leachate or are naturally occurring. As described below, this assessment is based on observed groundwater chemistries, chemical analysis of the CKD and native materials, and the hydraulic conditions. 5.1.1 Chemical Considerations The highest concentrations of barium are found in samples collected from the Group 3 wells (MW -4, MW- 6 and MW -7). These wells are located greater than 500 feet from CKD disposal area A2. Group 2 wells (MW -2 and MW -3) are located less than 100 feet from the CKD disposal area and have lower observed concentrations of barium. Likewise, observed TDS concentrations are higher in samples collected from the Group 3 wells than the Group 2 wells. This inverse relationship suggests barium and TDS concentrations reflect influence by native host materials and do not reflect influence from CKD leachate. If the CKD deposited in area A2 was an ongoing source for barium and TDS loading to the groundwater, higher concentrations would be expected closer to the CKD disposal area A2. Although TDS and barium concentrations in MW -4 increased during the 1998 and 1999 sampling, the concentrations have been stable since 2010. Although SPLP analysis is not designed to definitively predict long term water quality, it does provide an indication of the CKD leachate characteristics. The SPLP leachate pH values are greater than 12 for the CKD material and between 7 and 10 for the native materials. Groundwater pH values at the Site are between 7 and 9, which are similar to values observed in the wells prior to CKD placement in area A2, and do not show an increase over time that would be expected if the waters were being influenced by CKD leachate. In addition, the SPLP leachate concentrations were at least an order of magnitude higher for the CKD material than for the native materials for arsenic, barium, chromium, lead, lithium, selenium and thallium and the majority of major ions. Dissolved metals concentrations elevated above benchmark Golder is \10\81640a1 0400\ gwcharwellinstallfieldrep _fnl- 30apr14 \10381840a gwcharrpt _holcim- boettcher_fnl- 28apr14- with holcim etlits.tlocx Associates