2020-02-13_HYDROLOGY - M2008082 - Laserfiche WebLink

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Ready Mix Concrete Substitute Water Supply Plan February 13, 2020 Page 4 of 10 this SWSP approval period. Stage 4 will continue to be dewatered throughout the period of this SWSP. Stage 6C/6D - Mining at Stage 6C/6D will continue. The exposed groundwater surface area is currently 0.5 acre and will remain at 0.5 acre through the end of this SWSP approval period. Stage 6C/6D will be dewatered throughout the period of this SWSP. The projected maximum net evaporation volume during the period of January 2020 through December 2020 is 56.5 acre-feet, as shown in the attached Table 2, column 2. In addition to the evaporation, water is lost with the mined product removed from the mine sites. RMCC projected that they will produce 1,556,600 tons of gravel during the requested SWSP period, as shown in Table 2, column 3b. All of the gravel mined will be from within previously lined gravel pits within Stage 4 and 6C/6D; therefore, the production uses are limited to water used to wash the mined product, which is estimated to be 2 percent of the gravel weight for all production during the period of this SWSP. The water used for gravel washing is projected to total 22.9 acre-feet, as shown in Table 2, column 4. A slurry wall will be constructed around Stage 5 using water pumped directly from the South Platte River. The water used for the slurry wall construction is estimated to be 4.3 acre-feet per month from approximately June 2020 through November 2020 or 25.78 acre-feet total, as shown in Table 2, column 10. The estimated water used for dust suppression is 14.4 acre-feet in 2020, as shown in Table 2, column 5. RMCC will use water from Stage 1 or Stage 2 for dust suppression purposes. RMCC will dewater Stages 1, 2, 6A, 6B and 4 during the period of this SWSP. Additionally, dewatering at Stage 6C/6D will begin prior to 2020. The dewatering pumping volume is projected to be 14 ac-ft per day at each unlined pit and 0.5 ac-ft per day at each lined pit and will be continuous at one or more stages throughout the SWSP request. The dewatering volumes shown in Table 2, column 6 represent the combined dewatering for all stages. Stage 1 will release 180 acre-feet of previously stored water in March for maintenance and will then be filled with 100 acre-feet of water currently stored in Stage 2. Water will be delivered directly from State 2 to Stage 1 and will be metered. The additional refill volume of 70 acre-feet that will occur in Stage 1 will occur through groundwater infiltration in March 2020. Lagged depletions from the groundwater infiltration will be replaced under this SWSP. Stage 2 will release 40 acre-feet of water in April for maintenance and will be refilled during free river if it occurs in late 2020, otherwise Stage 2 will be refitted in 2021. The total consumptive use at the site for the period of this SWSP is 189.61 acre-feet. The dewatering pumping volume to be discharged to Big Dry Creek during the period of this SWSP is estimated at 18,096 acre-feet, as shown on the attached Table 2, column 6.