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Red Creek Quarry Baseline Water Investigation Section 6 <br /> <br /> <br />6-13 <br />DRAFT for review purposes only. Use of contents on this sheet is subject to the limitations specified at the end of this docu ment. <br /> <br />Figure 6-10. Time trend plot of dissolved selenium for surface and groundwater <br /> <br />Chlorine has several potential sources including usage of organochlorine pesticides, the degradation <br />of naturally occurring chlorine-bearing rocks, or industrial chemical such as polychlorinated biphenyls <br />(PCBs). Organochlorine compounds can persist in the natural environment for decades and be <br />transported long distances for the source (Singh, Singh, and Sillanpaa 2022). There is no known use <br />of pesticides on a large-scale on the Site. The likely source of the total chlorine measured in the <br />surface waters are past use of pesticides remaining in the hydrologic system of the Red Creek <br />drainage. Hydrogen sulfide can occur in water as a result of the microbial activity of sulfur reducing <br />bacteria or the decay of plant-based organic material. Dissolved sulfide concentrations within the <br />surface water samples are likely the result of the groundwater source discharging in Red Creek. <br />Groundwater dissolved sulfide concentrations are similar in concentration to the surface water <br />quality data (Figure 6-11). <br /> <br />Figure 6-11. Time trend plot of dissolved sulfide for surface and groundwater