2023-02-24_HYDROLOGY - M2004009 (2)

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ASCI Turnpike Mining Resources SWSP Page 2 of 7 February 24, 2023 In accordance with approach nos. 1 and 3, ASCI has indicated that a bond has been obtained for $1,114,000.00 through the DRMS for lining of this site to assure that depletions from groundwater evaporation do not occur in the unforeseen event(s) that would lead to the abandonment of the Pit. Depletions Projected depletions at the site consist of evaporative depletions, dust control, dewatering, and lagged depletions from past mining activities. Evaporation The Applicant anticipates that groundwater will be exposed within Cells 2A, 213, 5, and 6 as shown in Table A below. The area of exposed groundwater for the wash pond and settling pond in Cells 2A and 2B will remain 4.0 acres throughout the SWSP period. The pump basin and dewatering trench (1,060 feet x 6 feet) in Cells 5 and 6 will expose 0.75 acres. Table A: Ex osed Surface Area by Cell Acres Cell 2A Cell 2B Cells 5 and 6 Total Wash Pond Settling Pond Pump Basin Dewaterin Trench 2.0 2.0 0.6 0.15 4.75 The Applicant proposes to replace evaporation from exposed groundwater at the site based upon evaporation atlases in NOAA Technical Report NWS 33 and the SEO monthly distribution factors for sites below 6,500 feet, as shown in attached Tables 1 and 2 (attached). Gross annual evaporation at the gravel pit location is estimated to be 39 inches per year. 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 based on the data from the Longmont South NCWCD weather station (record 1994-2018). The net evaporation from the exposed water surface is estimated at 28.25 inches per year. Total evaporative depletions are estimated at 11.18 acre-feet during this SWSP period, as shown on Table 2 (attached). Computation of evaporation under this SWSP was reduced during the ice covered period. It was assumed that the ice covered period will occur during the months of December and January based on average monthly temperatures less than 32°F taken from the Longmont South NCWCD weather station (record 1994-2016). However, for the purpose of this SWSP, the Applicant shall replace the net evaporation depletions from the exposed groundwater surface area that may occur during the assumed ice covered period (the months of December and January) for any time that the pit is not completely covered by ice. Computation of the net evaporation during any time that the pit is not completely covered by ice shall be determined as the pro-rata amount of the monthly gross evaporation rate distribution amount identified in the State Engineer's General Guidelines for Substitute Supply Plans for Sand and Gravel Pits, subtracting the pro-rata amount of the effective precipitation for that period. Dust Control The Applicant projects that 1.76 acre-feet will be used in Cells 2A and 2B for dust control during this SWSP period, as shown in column 5 of Table 3 (attached).