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2021 Groundwater Monitoring Report <br />www.arcadis.com <br />2021 Holcim FINAL GWMR 1 <br />1 Introduction <br />Holcim (US) Inc. (Holcim) retained Arcadis U.S., Inc. (Arcadis) to sample the groundwater monitoring wells <br />adjacent to the cement kiln dust and alkali bypass dust disposal area (CKD disposal area) at the Holcim Portland <br />Plant quarry, located at 3500 Highway 120 in Florence, Colorado (site). The sampling was performed to fulfill the <br />requirements of the Colorado Division of Reclamation Mining and Safety (DRMS) as a result of a December 2007 <br />DRMS inspection, which is discussed further in Section 1.3. The sampling was performed on March 18, 2021. <br />This 2021 Groundwater Monitoring Report (report) describes the procedures used to measure the depth to <br />groundwater at all quarry monitoring wells and piezometers and to collect groundwater samples at selected <br />quarry monitoring wells. This report also presents the results of the groundwater depth measurements and <br />groundwater sample laboratory analysis. <br />The remainder of this section presents the site location and history of the site that is relevant to groundwater <br />quality. Section 2 describes the field activities for the measurement of groundwater levels and sampling of existing <br />monitoring wells. Section 3 presents results for the groundwater analyses and groundwater elevation <br />measurements. Section 4 presents the conclusions of the 2021 annual sampling event and provides <br />recommendations. Section 5 lists the references cited throughout this report. <br />1.1 Site Location <br />The Portland Plant (plant), which manufactures Portland cement, is located in Fremont County (Figure 1) on the <br />southern side of the Arkansas River. The quarry that supplies the limestone for the plant used in the <br />manufacturing process is located on the northern side of the Arkansas River. The total area of the site, including <br />the quarry, is approximately 3,400 acres. <br />1.2 Site History <br />Cement manufacturing operations at the site began in 1897. Prior to 2001, three long, wet kilns with a combined <br />cement production of approximately 937,000 tons per year (tpy) were in service. Cement kiln dust (CKD) is waste <br />material that was generated by the cement kiln and associated equipment. Using the wet kiln process, <br />approximately 25,000 to 100,000 tpy of CKD were generated during the production of cement at the site <br />(Resource Geoscience, Inc. [RGI] 1999). Historically, sludge from the nearby Fremont Sanitation District <br />wastewater treatment plant (WWTP) was added to the CKD disposal area as a daily cover. The sludge also <br />served as a means of dust control. <br />In 2001, the three wet kilns were replaced by one dry kiln with a clinker capacity of 1,873,898 tpy. In the dry kiln, <br />all of the dust generated within the kiln during the manufacturing process is recycled within the process. However, <br />during the production of low-alkali clinker, calcium chloride is added to the process to assist with removal of <br />alkalis from the raw material. Some of the alkalis are removed by taking a portion of the raw material out of the <br />process via the alkali bypass system. The alkali bypass dust (bypass dust) removed from the process is similar in <br />chemistry to the CKD that was historically disposed of and transported to the CKD disposal area in the quarry. <br />When possible, bypass dust is sold to customers to eliminate the need for disposal on site. Alternative uses for <br />the bypass dust must be approved by Holcim. Bypass dust is currently produced at a lower rate than CKD when