Laserfiche WebLink
Second Submittal <br /> 2.2.6 Local Water Quality <br /> It is well documented that surface and some groundwater in Northern Larimer County <br /> suffer from increased selenium concentrations (Elmund, 2014; Herr, 1977; Pierce, 2014), <br /> mostly sourced from oxidation of generally selenium-sulfide (selenium is in a reduced <br /> state)minerals dispersed throughout the Pierre shale. Where the Pierre shale outcrops and <br /> surface waters come into contact, the oxygen rich surface water oxidizes the reduced <br /> selenium minerals and produces more soluble selenium mineral phases (e.g., selenite, <br /> selenate), which are dissolved and transported in surface waters. Enhancing the <br /> mobilization of selenium is the erosion of the Pierre shale,which continually exposes fresh <br /> minerals while placing solid selenium minerals in the water column. <br /> The same oxidation potential exists for well oxygenated alluvial groundwater where it is <br /> in contact with the Pierre shale. However,the erosion potential does not exist and the only <br /> mechanism for moving the selenium into the alluvial groundwater system is molecular <br /> diffusion(which,is a slow process). Thus, alluvial groundwater generally does not exhibit <br /> the same concentrations as surface water unless it is sourced from a surface water with high <br /> selenium concentrations. <br /> LRM collected random samples from monitoring wells MW-2, MW-6 and MW-13, and <br /> from the Cache la Poudre River nearby. Laboratory reports are provided in Appendix B. <br /> All samples reported non-detect for selenium with the exception of MW-6 (0.043 mg/L). <br /> MW-6 had a trace of sediment in the sample, which is the likely source of the selenium. <br /> LRM also collected samples of the Pierre shale and subjected them to the Environmental <br /> Protection Agency's Synthetic Precipitation Leaching Procedure (SPLP) test. SPLP <br /> subjects soil/solid samples to direct contact with slightly acidic water to examine the <br /> potential for release of chemicals from the solid. The SPLP results indicated that of the <br /> four samples taken, one had the potential to release selenium (B20, 0.13 mg/L in the <br /> leachate). Lab reports are provided in Appendix B. No other metals were detected in the <br /> SPLP results. Implications of these results are described in section 7.1 <br /> Loveland Ready-Mix Concrete 9 Telesto Sohitions,Inc. <br /> 20180112 gom1wX—tuay2 ubmffaldmx January2018 <br />