2014-03-19_HYDROLOGY - M1979097 - Laserfiche WebLink

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Mr. Jared Dains Page 2 East Rigden Pit Substitute Water Supply Plan (M -79 -097) March 19, 2014 requirements. Additionally, at the time this SWSP expires, if there is no progress made on the operators behalf to bring this site into compliance, the SWSP may not be renewed which would result in Cease and Desist Orders against the mine site. Depletions Consumptive use at the East Rigden Pit ( "Fort Collins Parcel ") will consist of evaporative and operational losses. During the September 2013 floods a significant amount of surface water from the Cache La Poudre River inundated the low area of the Fort Collins Parcel. The water was pumped out by the end of December 2013. Since then only a minor amount of ground water approximately three acres are exposed within the Fort Collins Parcel. Evaporative losses are calculated based on exposed ground water surface area of 3.0 acres in the dewatering trenches and sumps. Net evaporative depletions were calculated using a gross annual evaporation of 39 inches from the exposed water surface, with a credit of 8.78 inches for effective precipitation. Computation of evaporation under this plan was reduced during the ice covered period. You have assumed the ice covered period to occur during the months of December, January and February based on average monthly temperatures less than 32 °F taken from Windsor weather station. The ice covered periods may be used to reduce the amount of evaporative losses that need to be replaced; 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 (December, January and February) 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. The net depletion of ground water due to evaporation of exposed ground water surface was calculated to be 6.80 acre -feet for this plan period. Pursuant to § 37- 90- 137(11)(b), C.R.S. and 2009CW49, a gravel pit operator or property owner does not need to replace depletions that occur due to evaporation from ground water exposed prior to January 1, 1981 (Pre -81) as a result of open mining of sand and gravel, regardless of whether mining continued after December 31, 1980 (Post -80). The Previous SWSP approved for the East Rigden Pit recognized 25 acres as being a Pre -81 exposure. The East Rigden Pit's Pre -81 exposure locations have previously been set and are not allowed to be relocated to other areas of ground water exposure within the gravel pit boundary. According to the attached Figure 1 only 2 acres of the Pre -81 exposure are located within the Fort Collins Parcel. Operational losses are estimated to occur due to diversion and consumption of water for embankment and liner construction, dust control and reclamation irrigation. Although material is being excavated from the Fort Collins Parcel, the material will be used to fill elsewhere in the pit or adjacent to the pit and therefore it was assumed that there would be no water loss associated with the mined material. The water for embankment and liner construction is estimated at approximately eight million gallons per months from March through December or 220.96 acre -feet during the SWSP period. The water lost for dust control and reclamation irrigation is estimated to be approximately 500,000 gallons per months from March through December or 13.81 acre -feet during the SWSP period. The total operational looses are estimated to be 234.77 acre -feet during the SWSP period. The estimated monthly depletions due to evaporation and operational losses (241.57 acre -feet) during the SWSP period are shown on the attached Table 1.