2009-02-04_HYDROLOGY - M1977522 - Laserfiche WebLink

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Ms. KC Hallett January 27, 2009 Page 2 C depletions from April through October were calculated based on an exposed surface area of 9.6 acres and were determined to be 23.1 acre-feet. The evaporative depletions from November through March were based on an exposed surface area of 29.7 acres and were determined to be 7.1 acre-feet. Note, that after the dewatering pumps stop, the river will experience a net depletion as the pits gradually fill. The Applicant is hereby notified that the depletions that will have an effect on the stream as a result of refilling the pit between November and March, must be addressed in any subsequent SWSP renewal for this pit. Computation of evaporation under this plan from November through March was also reduced during the ice covered period. You have assumed the ice covered period to occur during the months of December through February, based on the average temperatures of 27.4°F for December, 26.0°F for January and 30.3°F February; taken from the Greeley weather stations (053533 and 053546) for the time period from 1893 through 2005. 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 through 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* ,6 18tate 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. You, have provided a monthly breakdown of the annual depletions totaling 30.2 acre-feet of evaporative.aos%,0.8 acre-feet of water used and consumed for dust control, 2.9 acre-feet of water lost with 100,000 tons of mined product, 3.1 acre-feet of water used in concrete production, and 0.11 acre- feet of water used for drinking and sanitary purposes. The water used for drinking and sanitary purposes is to be withdrawn from well permit no. 57724-F. No phreatophyte credit has been applied to this plan. A stream depletion model was used to determine the lagged depletions to the Cache La Poudre River. The following parameters were used in the model: transmissivity (T) = 120,000 gallons per day per foot, specific yield (SY) = 0.2 (which is typical for an alluvial aquifer), the distance of the exposed ground water to the river = 250 feet, and the location of the parallel impermeable boundary was estimated to be 4,300 feet from the stream. Note, that due to a change in administration of evaporation from ground water exposed to the atmosphere prior to 1981, pre-1981 credits will no longer be allowed for gravel pits which exposed ground water to the atmosphere prior to 1981 and were actively mined on or after January 1, 1981. Accordingly, evaporative depletions for such gravel pits will need to be replaced from the entire surface area of the ground water exposed in the pits. In order to allow owners and operators of the affected pits time to comply with this change in the administration requirements, the owners and operators will have until January 1, 2010 to comply with the replacement requirements. The Applicant is hereby notified that the evaporation from the 6.1 acres of ground water exposed prior to 1981 must be replaced after January 1, 2010 in any subsequent SWSP renewal for this pit. Replacements The sources of replacement water to be used for this plan are 1) fully consumable replacement water leased from the City of Greeley, and 2) historical stream depletions from the dry-up of lands