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Red Creek Quarry Baseline Water Investigation Section 6 6-11 DRAFT for review purposes only. Use of contents on this sheet is subject to the limitations specified at the end of this document. 6.2.2 Elevated Constituent Concentrations in Surface Water Surface water data were compared to the water quality standards for COARU14A segment based on the watershed designation for Red Creek (Figure 6-9) from the Colorado Department of Public Health and Environment Clean Water GIS website (https://cdphe.colorado.gov/clean-water-gis-maps). Surface water data were elevated with respect to the standards for several total and dissolved metals/metalloids, nitrite, total phosphorus, total chlorine and dissolved sulfide (Appendix H). Results of the comparison to water quality standards are summarized in Table 6-1. The elevated metal/metalloid results are mainly from the Stilling Well sample collected during the first quarterly sampling event (August 2022). Results from the Stilling Well are likely reflective of shallow alluvial <br />water in contact with the creek bed sediments and no t the water flowing within Red Creek. High <br />turbidity from the Stilling Well also likely affected the total and dissolved metal/metalloid concentrations of the sample. Concentrations of dissolved selenium, dissolved sulfide, total chlorine, and Escherichia coli (E. coli) had more than one elevated surface water quality result (Appendix H). E. coli are bacteria found in the lower intestines of humans and animals. The presence of E. coli in the surface water samples is likely the result of fecal matter from cows or other animals close to and within Red Creek. Evidence of animals (cows and other wildlife) was observed over multiple sampling events in the area of all three surface water sites. Time trend plots were generated of dissolved selenium to evaluate changes in concentration (Figure 6-10). Data from SW RC1 had lower concentrations of dissolved selenium during May and July of 2023 than the previous two quarters. Location SW RC1 is a shallow pool of water without much flow (mostly stagnant) with a silty bottom that can become suspended during the sample collection (Photo 6-2). The lower concentrations of dissolved selenium may be the result of increased direct precipitation during the days to weeks prior to the sampling events or the result of heterogeneity of the sample source due to suspended solids from the pool bottom becoming entrained in the sample during collection. Photo 6-2. Surface water location SW RC1