2016-02-03_HYDROLOGY - M1979191 - Laserfiche WebLink

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Middle Poudre Combined SWSP Page 2 of 8 February 3, 2016 depletions due to past mining and dewatering operations at the Kyger Pit were replaced by the end of 2015 and the site is no longer required to be covered under a SWSP. Depletions Three Bells Pit Consumptive use at the Three Bells Pit will consist of evaporation, water used for dust control, and water lost in the mined product. The Three Bells Pit consists of two primary mining cells, the "Veldman" parcel to the southeast and the "DiTullio" parcel to the northwest. Mining operations have been completed at the Veldman parcel and mining operations have shifted to the DiTullio parcel. The clay liner for the Veldman parcel was approved by the State Engineer's Office as meeting the design standard for liners in a letter dated March 6, 2015, and is now classified as a lined reservoir in accordance with the 1999 SEO Guidelines (River Bluffs Lake, WDID 0303324). The DiTullio parcel will continue to be dewatered and mined throughout this plan period. The Applicant has confirmed that meters have been installed on all dewatering systems, and meter readings will be included in the monthly accounting. The recorded volume must be included in the monthly accounting for this plan. The exposed surface area at the site is currently estimated to be approximately 17.5 acres, consisting of unlined ponds and dewatering trenches. The Applicant anticipates that 12.0 acres of exposed ground water located within three cells located east of the Cache la Poudre River will be backfilled by September 2016, leaving 5.5 acres of exposed ground water for the remainder of the plan period. Net evaporative depletions were calculated as 33.19 acre-feet for this plan period using a gross annual evaporation of 39 inches from the exposed water surface, with a credit of 8.78 inches for effective precipitation. You have assumed an ice covered period to occur during the months of January, February, and December 2016 and have reduced the computation of evaporation accordingly. However, for the purpose of this SWSP, the Applicant shall replace the net evaporation depletions from the exposed ground water surface area that may occur during the assumed ice covered period (January, February, and December) 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. A total of 732,725 tons of material is anticipated to be mined at the site during this plan period. Much of the material will be washed, therefore for the purposes of this SWSP it is assumed that all of the mined material will be washed. For material mined below the water table in a dewatered state and washed, the water retained in the mined product is considered to be 4.0% of the mined material by weight. This results in a groundwater loss of 21.57 acre-feet You have estimated that 19.33 acre-feet of water will be used for dust control purposes during this plan period. Previous SWSPs have indicated that some water use for dust control may occur off-site. Any use of the water for dust control purposes, either at this site or at another location, must continue to be related to gravel mining operations. The total consumptive use of ground water at the Three Bells Pit (including evaporative and operational losses) is estimated to be 91.58 acre-feet for this plan period, as detailed in the attached Appendix A.