2023-08-29_HYDROLOGY - M2015030 - Laserfiche WebLink

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Chavers Mining Resources Substitute Water Supply Plan 2023 Page 2 of 8 August 29, 2023 water resources. The April 30, 2010 letter from DRMS requires that the Applicant provide information to DRMS to demonstrate they can replace long term injurious stream depletions that result from mining related exposure of groundwater. The DRMS letter identifies four approaches to satisfy this requirement. In accordance with approach nos. 1 and 3, the Applicant has indicated that a bond has been obtained for $1,848,166 through the DRMS for lining of this site to assure that depletions from groundwater evaporation do not occur in the unforeseen event, or events that would lead to the abandonment of the Pit. Depletions The projected depletions for the period of this SWSP consist of net evaporation from exposed groundwater surface area, water removed in the mined product, dust suppression, dewatering, and concrete production. Depletions are calculated for the period of August 1, 2023 through December 31, 2023 as well as for August 1, 2023 through July 31, 2024 (annual or per year depletions) subject to approval condition no. 1. Evaporation Water for dewatering, gravel washing, and dust control will be provided by a series of wash ponds that expose groundwater. The Applicant anticipates that a total of 18 acres of water surface will be exposed at the site in the pump basin (14.85 acres), dewatering trench (0.15 acres) and wash ponds (3.0 acres). 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 Table 2. Gross annual evaporation at the gravel pit location is estimated to be 44 inches per year. Net evaporation is defined as gross evaporation minus 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 Brighton 1 NE (record 1974-2021) NOAA weather station. The total net evaporation is 48.68 acre-feet per year, and 18.47 acre-feet for the period of August 1, 2023 through December 31, 2023, as shown on attached Table 2. Computation of evaporation under this SWSP was reduced during the ice covered period. It is assumed 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 Brighton 1 NE (record 1974-2023) NOAA weather station. 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 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 estimated water used for dust suppression per year totals 1.25 acre-feet per year and 0.52 acre-feet for the period of August 1, 2023 through December 31, 2023, as shown on attached Table 3. Mined Product In addition to the evaporation, water is lost with the mined product removed from the mine site. The Applicant projects that they will produce 650,000 tons of gravel each year or 261,000 tons for the period of August 1, 2023 through December 31, 2023. Gravel mined will be in a dewatered state and will be washed, therefore the groundwater 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 19.12 acre-feet per year