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Dowe Flats Quarry Site Description and Future Mining Impact Analysis <br /> 1 Introduction <br /> The CEMEX, Inc. Dowe Flats Quarry(Dowe Flats) is a limestone quarry located near the Town <br /> of Lyons in Boulder County, Colorado. Dowe Flats currently operates under Boulder County <br /> Special Use Permit(SUP)number SU-93-14 which is set to expire in the near future. CEMEX, <br /> Inc. is seeking to amend their SUP to extend mining within the current footprint for an additional <br /> 15 years. Habitat Management, Inc. (Habitat Management)was contracted to prepare the <br /> following report to describe existing site conditions and evaluate the ecological impacts of <br /> continued mining. <br /> Habitat Management scientists,natural resources consultants, and field crews have provided <br /> services to CEMEX, Inc. at this location since 2010. Our personnel are intimately familiar with <br /> the site conditions, site history,reclamation, and permitting details. <br /> This report includes descriptions of streams, irrigation ditches, areas subject to flooding, lakes, <br /> high ground water areas, topography, current land use, vegetation communities,wetlands, <br /> climatology, and wildlife habitats. Additionally, each of these site features was evaluated to <br /> consider the ecological impacts that would result from continued mining. <br /> 2 Site Features <br /> The area that is currently permitted under SU-93-14 includes the Dowe Flats property itself and a <br /> Partition Agreement Lease area around the Dowe Flats property owned by Boulder County Open <br /> Space and leased to CEMEX, Inc. as a buffer. The original permit application included 1,911 <br /> acres; however, approximately 101 acres were removed over the years due to property sales <br /> resulting in a current permit boundary of 1,810 acres. With the proposed amendment to the SUP, <br /> CEMEX, Inc. is planning to reduce the permit area to only include the Dowe Flats property <br /> itself, which is 709 acres, a 61%reduction in area. (Figure 1). This report focuses on the Dowe <br /> Flats Property only. <br /> 2.1 Streams <br /> Saint Vrain Creek is the only perennial waterway near the permit area, and it does not intersect <br /> the Dowe Flats boundary. The conveyor corridor crosses Saint Vrain Creek in an elevated and <br /> fully enclosed location. No activities proposed in the permit amendment application will impact <br /> Saint Vrain Creek. <br /> There are several intermittent streams shown crossing Dowe Flats on the Boulder County GIS <br /> database (Boulder County 2020a). These drainages are primarily fed by seepage from the St. <br /> Vrain Supply Canal and agricultural irrigation. No activities proposed in the permit amendment <br /> application will have new impacts on these drainages. <br /> 2.2 Irrigation Ditches <br /> There are several active irrigation ditches that flow across the permit area. The Supply Ditch,the <br /> Highland Ditch, the Rough and Ready Ditch, and the Palmerton Ditch all cross the Dowe Flats <br /> property south of the active mining area. Several of these ditches cross under mine access roads <br /> in culverts. Berms and other stormwater management strategies are in place to prevent runoff <br /> from these roads from entering the irrigation ditches. No activities proposed in the permit <br /> amendment application will have new impacts on these waterways. <br /> Habitat Management, Inc. 1 May 2, 2022 <br />