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Mr. Michael Toelle <br />Holcim US, Inc. <br />January 31, 2024 <br />Page 2 <br />Holcim RCQ Letter Report 20240131 <br />investigation as to the validity, completeness, or accuracy of such information provided <br />by third-party sources. For the purposes of this assessment, such third-party information <br />is assumed accurate unless contradictory evidence is noted, and BC does not express or <br />imply any warranty regarding information provided by third-party sources. <br />Precipitation data was downloaded from the NOAA Precipitation Frequency Data Sever <br />(PFDS) website based on the NOAA (2013) Atlas of the United States, Volume 8, Version <br />2.0: Midwestern States. The hydrologic properties of the Codell Sandstone were devel- <br />oped from slug tests conducted during a baseline sampling event in May 2023. The rele- <br />vant soil series data and descriptions from the USDA NRCS Soil Survey of Fremont and <br />Pueblo Counties, Colorado (USDA 1995) are in Attachment A. <br />Hydrologic Analysis <br />RCQ (the Site) is located approximately 15 miles west of Pueblo, Colorado along High- <br />way CO-96 and encompasses approximately 3,851 acres. Red Creek flows northeast <br />through the Site into the Arkansas River approximately 2 miles northeast of the Site. Alt- <br />hough the Red Creek channel will not be altered by mining operations nor contribute <br />flow to the reclaimed pits, there are drainage areas south of the Site that will contribute <br />stormwater runoff to the Site (predominantly in the area of the backfilled pit). <br />BC calculated the volumetric runoff for the Site using the hydrologic modeling software, <br />HydroCAD. The precipitation depth from a NOAA Atlas 5-year, 24-hour, SCS Type II storm <br />event was used in the model. The contributing drainage basins were delineated using <br />the proposed reclaimed pit and Site topography, provided by Holcim, in conjunction with <br />an ArcGIS LandSat digital elevation model (DEM) to capture all contributing off-site <br />drainage. Figure 1 shows the extent of the contributing drainage areas. <br />Calculations were performed using TR-55 runoff methodology as required by the USDA <br />NRCS for sites greater than 20 acres. Curve Number’s associated with brush in fair con- <br />dition were applied to the hydrologic soil group (HSG) generated from the USDA NRCS <br />Soil Survey. Attachment A contains the results report summary. Attachment B contains <br />the HydroCAD model output files. <br />