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Red Creek Quarry Baseline Water Investigation Section 6 <br /> <br /> <br />6-9 <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 />6.2 Constituents with Naturally Occurring Elevated Concentrations <br />One objective of the RCQ baseline water quality project was to establish the background level <br />concentration of regulated constituents. Background level is defined as “the level of any parameter <br />in the groundwater within a specified area as determined by representative measurements of the <br />groundwater quality unaffected by activity” (WQCC 5 CCR 1002-41.3 (3)). A comparison of <br />established surface and groundwater water quality standards was conducted to identify analytes <br />with naturally occurring elevated concentrations and to serve as a useful frame of reference for <br />understanding background level water quality. <br />The use of water quality standards and criteria in this report is for technical analytic purposes; it <br />should not be interpreted to include any legal or regulatory compliance conclusions, or to suggest <br />any sampling point or other location is a discharge or other regulatory point of compliance. <br />Highly turbid sample data may be overestimating the concentrations of both the total and dissolved <br />metals because filtering does not remove all suspended particulates (Puls and Barcelona 1989). <br />Because of the occurrence of suspended particulate matter in numerous groundwater samples and <br />upstream surface water samples, assessments of baseline water quality at the Site based only on <br />total metals/metalloids concentrations alone would likely overstate the extent of mobile <br />constituents. Turbidity field measurements, TDS, and total suspended solids concentrations were <br />reviewed when evaluating the metal/metalloid concentrations for surface and groundwater data. <br />6.2.1 Elevated Constituents Concentrations in Groundwater <br />Groundwater data were compared to the drinking and agricultural water quality standards listed <br />under WQCC 5 CCR 1002-41 to identify constituents with naturally occurring elevated concentrations <br />(Appendix H). Scatter plots of groundwater data were generated to evaluate the spatial variability of <br />elevated constituents (Figure 6-8). The red lines on the plots indicate the groundwater standard <br />concentration for each constituent. Sulfate concentrations for all ground water samples exceed the <br />drinking water quality standard of 250 mg/L; therefore, there is no line to indicate the sulfate <br />drinking water standard on the plots. <br />Naturally occurring elevated concentrations of selenium, uranium and sulfate have been identified <br />within lithological members of the Niobrara Formation in the Arkansas River valley near the Site <br />(Arnold et al. 2016; Bern and Stogner 2017; Miller et al. 2010). Elevated concentrations of iron and <br />manganese have been measured in shallow alluvial groundwater samples collected along the <br />Fountain Creek drainage (Arnold et al. 2016). The groundwater data in Figure 6-8 show a range in <br />concentrations across the Site: <br />• Well 1 has the highest concentrations dissolved selenium and dissolved uranium. <br />• Well 3 has the highest concentrations in dissolved manganese and sulfate. <br />• Well 4 has the highest concentrations of gross alpha and dissolved iron.