2025-09-18_HYDROLOGY - M1999034 - Laserfiche WebLink

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Holcim South Platte Combined SWSP September 18, 2025 Plan IDs 3614, 4773, 3624, 4772, 4616, 3437, 3376, 3650, 3668, 5475, 5829, &t 6243 Page 9 of 37 27.1 DPG Pit 51.3 (920,300 2.56 0 80.9 79.40 0` 79.40 tons) Distel Pit Oa 0 1.5 0 1.5 1.54 0 1.54 Tull Pit 10.3 0 2.0 0 12.3 21.09 0` 18.98 Irwin- 16.6 6.4 (563,400 1.54 0 24.6 23.93 0` 23.93 Thomas Pit tons W.W. Farms 178.6 0 1.0 4.6 184.2 184.7 0` 184.74 Pit F-Street Pit 102.0 0 0 0 102.0 101.5 0 101.52 Total -- 772.0 803.52 a Evaporation is replaced by the City of Longmont under their augmentation plan decreed in water court case no. 09CW271. b Lagged Dewatering Depletions, as shown in the table, are from past dewatering operations that have ceased but continue to impact the stream system. So long as the pit is continuously dewatered, the water returned to the stream system is considered to be adequate to offset depletions attributable to the dewatering. A stream depletion model using either the Glover method, or Stream Depletion Factor (SDF) method (for the Brighton Pit) was used to calculate the lagged depletions to the river. The Glover method uses four aquifer input parameters for each site as follows: 1) X - distance (ft) from centroid of exposed groundwater to river, 2) W - distance (ft) from the aquifer boundary through the well (gravel pit) to the river channel, 3) T - transmissivity of the alluvial aquifer (in gallons per day per foot) between the well (gravel pit) and the river, and 4) S - specific yield (0.2 was used for all sites). The parameters used in the model for each site are listed in Table D below. Table D - Aquifer Characteristics Site Name T (gal/day/ft) X (ft) W (ft) OF (days) Jeronimus Pit 100,000 1,600 23,000 - Hazeltine Pit 100,000 1,200 23,000 - Brighton Pit - - - 10 Tucson South Pit 75,000 1,600 4,600 - Wattenberg Pit 80,000 1,200 5,500 - Platte Valley Pit 150,000 1,400 7,400 -