2011-08-30_HYDROLOGY - M2009018 - Laserfiche WebLink

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Cheryl Signs, P.E. Heintzelman Pit Depletions Page 2 August 26, 2011 In accordance with approach no. 4, you have provided an affidavit dated November 1, 2010 that dedicates five of the Applicant's shares of GIC water and 4 shares of the Rural Ditch water and portions of the water rights decreed in case no. 2001CW274 as replacement water solely for this SWSP, Durham Pit SIIVSP (M78 -056), Kurtz Pit SWSP (M99 -006), and Western Sugar Pit (M10 -049) for as long as there are depletions at these gravel pit sites or until such time as another replacement source is obtained. A copy of the affidavit is attached to this letter. For the purposes of this SWSP, this affidavit will be accepted for the dedication of the shares; however, if the State Engineer determines that a different affidavit or dedication process is necessary to assure proper dedication of the shares, additional information may be required prior to future SWSP approvals. The anticipated net depletions for this SWSP are 290.19 acre -feet per year. The SWSP anticipates that a total of 105.44 acres of water surface will be exposed at the site if dewatering ceases. The evaporation calculations were based on the entire exposed surface area in the event that the dewatering ceased and this SWSP will cover replacements for depletions associated with the 105.44 acres. However, for purposes of accounting, depletions will be calculated based on the ground water surface area actually exposed at the site. You have provided a monthly' breakdown of the annual depletions, which include 263.28 acre - feet of net evaporative Toss, 23.55 acre -feet of water lost with the mined product (which represents 800,000 tons of mined product), and. 3.36 acre -feet of water used for dust control. In addition, the operator has included plans to maintain the historical return flows back to St. Vrain Creek from the irrigation practices that occurred on the site prior to mining (see the attached Reservoir Operation Study Tables for details on releases to maintain historical return flows). Computation of evaporation under this SWSP was also reduced during the ice covered period. You have assumed the ice covered period will occur during the months of December, January, and February based on the Longmont weather station average temperatures of 29.7 °F for December, 26.5 °F for January, and 31.0 °F for February. 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 (the months of December, January, and February) for any time that the exposed ground water in the pit is not completely covered by ice. Computation of the net evaporation during any time that the pond 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 IDS AWAS stream depletion model was used to determine the lagged depletions from dewatering, evaporation and operational losses to Saint Vrain Creek. The aquifer characteristics used in the model are: transmissivity (T) = X100,000 gallons per day per foot and specific yield (SY) = 0.28 (based on the USGS Water Supply Paper 1662D). The nearest stream is a natural seepage ditch that originates uphill from the site and flows continuously through the west side of the property to Saint Vrain Creek. The distance of the exposed ground water to the stream = 225 feet, and the location of the parallel impermeable boundary was estimated to be 1,300 feet from the stream. For purposes of this SWSP, the distance of the exposed ground water to the river X is accepted; however, should the Applicant seek to renew this SWSP, the Applicant must calculate the depletions with the X value measured from the centroid of the pond.