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Mr. Michael Toelle <br />Holcim US, Inc. <br />January 31, 2024 <br />Page 4 <br />Holcim RCQ Letter Report 20240131 <br />Table 1. Drainage Areas and Runoff Volumes <br />Area <br />Drainage Area <br />(acres) <br />Runoff Volume <br />(acre-feet) <br />Backfilled pit 3,971 46.94 <br />Pit 1 171 1.93 <br />Pit 2 561 5.32 <br />Pit 3a 1,306 18.38 <br />Pit 3b 385 4.49 <br />The resulting size of the stormwater pools was determined by dividing the runoff volume <br />by the planar surface area for each area where the stormwater would collect (i.e., the <br />backfill pit surface and the exposed pit bottoms). Figure 2 shows the approximate extent <br />of the stormwater pools resulting from a 5-year, 24-hour rainfall event. <br /> <br /> <br />Figure 2. Stormwater Pools <br />Table 2 summarizes the corresponding stormwater pool areas and depths in each area. <br /> <br />Table 2. Stormwater Pool Sizes <br />Area <br />Pool Area <br />(acres) <br />Pool Depth <br />(feet) <br />Backfilled pit 370.8 0.127 <br />Pit 1 113.2 0.017 <br />Pit 2 226.4 0.023 <br />Pit 3a 99.0 0.186 <br />Pit 3b 30.7 0.146