2021-07-01_HYDROLOGY - M2015030 - Laserfiche WebLink

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Chavers Mining Resources Substitute Water Supply Plan Page 3 of 7 July 1, 2021 Mined Product and Operational Losses In addition to the evaporation, water is lost with the mined product removed from the mine site. The Applicant projects that they will produce 700,000 tons of gravel for each year. Gravel mined will be in a dewatered state and will be washed, therefore the ground water lost with the mined product during this period is estimated at 4 percent by weight. The water lost with the mined product is projected to total 20.61 acre-feet per year, as shown in Table 3, column 2. Water for gravel washing and dust control will be provided by a series of wash ponds that expose groundwater. The estimated water used for dust suppression per year total 1.25 acre-feet as shown in Table 3, column 3. As mentioned above, the water used for concrete production will be provided by the alluvial well (permit no. 80120-F). Assuming 30 gallons of water/cubic yard and 154,000 cubic yards of concrete production, the estimated water used for concrete production is 14.18 acre-feet per year, as shown in Table 3, columns 4 Et 5. Total Consumptive Use and Lagged Depletions Annual depletions include evaporative losses of 2.63 acre-feet per year for the pump basin and dewatering trench, 6.07 acre-feet per year for the wash ponds, 20.61 acre-feet of water lost with the mined product, 1.25 acre-feet of water used for dust control, and 14.18 acre-feet of water used for concrete production. The total consumptive use at this site is 44.74 acre-feet per year. The IDS AWAS stream depletion model was used to determine the lagged depletions from evaporation, operational losses, and the alluvial well to the South Platte River. The model parameters used are shown in Table A below. Table A. IDS AWAS Model Parameters Distance from Distance from d/ft) Well Name Boundary boundary to Transmissivity Specific Yield well to Condition stream (ft) (gp stream (ft) Aggregate Mining Alluvial Aquifer 7,500 85,000 0.2 350 Aggregate Processing Alluvial Aquifer 7,500 85,000 0.2 1,275 Concrete Production Alluvial Aquifer 7,500 85,000 0.2 1,045 The total lagged depletions per year equal 43.25 acre-feet, of which 22.70 acre-feet are associated with the evaporation and mining operation, 7.29 acre-feet are associated with the evaporation from the wash pond and dust control, and 13.26 acre-feet are associated with the water pumped from the alluvial well, as shown in Table 4. Dewatering Dewatering at this site will produce delayed depletions to the stream system. As long as the pit is continuously dewatered at a relatively constant rate, the water returned to the stream system should be adequate to offset the depletions attributable to the dewatering operation. Dewatering operations must be measured by totalizing flow meters that can accurately show the monthly volume of dewatered water that is pumped and returns to the stream. Should it be determined by the Water Commissioner or Division Engineer that dewatering water is being diverted for any purpose by the operator and accounting is not adequate to show that 100 percent of the dewatering water is returned back to the South Platte River, the Applicant will need to account for any lagged dewatering depletions at the site. In addition, if it is determined by the Water Commissioner or Division Engineer that the pit is not continuously dewatered at a relatively constant rate then the Applicant must track depletions and dewatering return