2022-01-13_HYDROLOGY - M1997054 - Laserfiche WebLink

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Jeffrey A. Clark January 13, 2021 Page 2 of 6 This SWSP continues to be approved pursuant to section 37-90-137(11), C.R.S., and this section allows approval of SWSPs for open mining of sand and gravel. The prior SWSP approved on February 24, 2021, indicated that depletions resulting from granite mining operations would not be approved pursuant to §37-90-137(11); however, based on additional information provided by the Applicant and BBA Water Consultants, the granite is mined, processed, and used for gravel and other construction materials. For the purposes of this SWSP, this granite mining operation is approved pursuant to section 37-90-137(11). In accordance with the letter dated April 30, 2010 from the Colorado Division of Reclamation, Mining, and Safety ("DRMS"), mining operators must comply with the requirements of the Colorado Reclamation Act and the Mineral Rules and Regulations for the protection of water resources. The April 30, 2010 letter from DRMS requires that you provide information to DRMS to demonstrate you can replace long term injurious stream depletions that result from mining-related exposure of groundwater. In accordance with approach nos. 1 and 3, you have indicated that a bond has been obtained for $1,145,736 through DRMS to assure that depletions from groundwater evaporation do not occur in the unforeseen event, or events, which would lead to the abandonment of the Pit. In addition, Martin Marietta Materials owns and has dedicated five shares of Twin Lakes Reservoir and Canal Company to cover these potential long-term depletions. Martin Marietta Materials must continue to commit those shares to this plan until such time as the State Engineer authorizes the release of this commitment. DEPLETIONS The depletions that result from the mining operation over the period of this SWSP include dewatering, evaporation, and mining operational losses (including water retained in product hauled off site). Evaporation losses will result from the exposure of groundwater in the settling ponds, an aggregate washing pond, and dewatering trenches. The maximum exposed water surface area during this SWSP period is 5.0 acres. Gross annual evaporation at the mining operation is estimated to be 46.0 inches per year and the monthly distribution is as depicted on the attached Table 1. Net evaporation is defined as gross evaporation less the consumptive use of water by vegetation that naturally occurred at the site prior to construction of the pit. The historical consumptive use was assumed to be equal to the effective precipitation, which was estimated as 70% of the 12.51 inches of average annual precipitation based on data from the Canon City weather station over the period 1893 through 2016. The net evaporation volume for the exposed water surface is 15.51 acre-feet per year with a monthly distribution as shown on the attached Table 1. Table 1 shows a monthly breakdown of the depletions under this SWSP on the attached Table 2, which includes 15.51 acre-feet of net evaporative loss, 8.90 acre-feet of water lost in product (based on an estimated 605,000 tons of washed aggregate and 192,600 tons of unwashed aggregate), and 22.41 acre-feet for on-site dust control, for a total consumptive use of 46.36 acre-feet. The IDS Alluvial Water Accounting System ("AWAS") stream depletion model was used to determine the lagged depletions from dewatering, evaporation and operational losses to the Arkansas River.