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<br /> <br />Portland Limestone Quarries (M-1977-344) Permit Amendment-02 <br />Holcim US Inc, 3500 Highway 120, Florence, CO 81226 Revised pursuant to preliminary adequacy review November 20, 2023 <br />Phone (719) 288-1443 www.holcim.us 75 <br />quarry, the top mine bench will be setback 25 feet from the base of the pole with setback in the quarry <br />floor up to 165 feet due to 1H:1V bench slope. <br />2.4.8 Water Diversions or Impoundments <br />Water impoundments will not be needed since water detention is not anticipated in the quarry. In the event <br />groundwater is encountered, it will routed toward Red Creek and ultimately discharge into the Arkansas <br />River. <br /> <br />Precipitation runoff resulting from a 5-year, 24-hour storm event was calculated to determine the volume of <br />precipitation that would infiltrate within 72-hours of the storm event (Appendix 4.11). Results of the limited <br />hydrologic analysis indicate accumulated water from a 5-year storm event in the eastern portion of the <br />reclaimed pit will likely not infiltrate within 72 hours. This limited hydrologic analysis will be conducted on <br />each mine block as the mine progresses eastward to determine the need and location of infiltration <br />galleries. <br /> <br />When mine blocks are identified where infiltration will not occur within 72-hours of a storm event, <br />infiltration galleries will be constructed to enhance infiltration in areas of the quarry where stormwater is <br />likely to migrate or it will be diverted to Red Creek. The infiltration galleries will be constructed by <br />excavating into the sandstone to increase the permeability and backfilling the excavation with coarse rock <br />(Figure 2.4.8-1). The location and specific construction of the infiltration galleries will be verified and <br />modified as necessary. <br /> <br /> <br />Figure 2.4.8-1: Example schematic of an infiltration gallery (Modified from Normal et al 1977) <br />