2021-08-17_HYDROLOGY - M2016085 - Laserfiche WebLink

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NCCI Bennett Gravel Pit SWSP Page 2 of 6 August 17, 2021 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 $1,005,627.00 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 The projected depletions for the period of this SWSP consist of net evaporation from exposed groundwater surface area, water removed in the mined product, dewatering and dust suppression. Evaporation The Applicant anticipates that a total of 8.51 acres of water surface will be exposed at the site outside of the north cell. The Applicant anticipates that the Bennett Pit liner will be approved by December 2021, therefore no evaporative depletions will occur in January and February 2022. The Applicant proposes to replace evaporation from exposed groundwater at the site based upon evaporation atlases in NOAA Technical Report NWS 33 and the State Engineer's Office (SEO) monthly distribution factors for sites below 6,500 feet. Gross annual evaporation at the gravel pit location is estimated to be 44.00 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 Brighton NOAA weather station (record 1978-2017). The net evaporation from the exposed water surface is estimated at 21.8 acre-feet. Water Lost from Mined Product In addition to evaporation, water is lost with the mined product removed from the mine site. The Applicant projects that they will produce 411,357 tons of gravel during the SWSP period with all excavation occurring outside of the north cells lined boundary. 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% by weight. The water lost with the mined product is projected to total 12.1 acre-feet during the SWSP period, as shown in Table 2 (attached). Dust Suppression The estimated water used for dust suppression during the SWSP period totals 4.8 acre-feet, as shown in Table 2 (attached). Dewatering Dewatering will occur within the lined boundary during the SWSP period. For purposes of this SWSP, the Applicant has accounted for the lagged depletions which occur due to dewatering which historically occurred and will occur between March 2021 and June 2021. The total amount of water pumped for dewatering purposes is 108.6 acre-feet for this SWSP period. Water discharged to the stream as a result of dewatering during the period of March 2021 through June 2021 exceeded the lagged depletions from the dewatering operation. This results in a credit to the stream that will be used to