2010-02-24_HYDROLOGY - M2002120 - Laserfiche WebLink

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Andy Rodriguez February 22, 2010 Page 2 Depletions Currently 6.23 acres of ground water surface is exposed at the Bernhardt pit within the settling ponds. Consumptive use from the operation of this site consists of 3.33 acre-feet for on-site dust control, 1.23 acre-feet used in the production of 10,000 tons of concrete and 17.94 acre-feet of evaporation from the 6.23 acres of exposed lake surface. There is no aggregate production proposed for this plan period. The total consumption at this site during the period of this plan from mining operations is 22.50 acre-feet. Dewatering at the site commenced in October 2003 at a rate of 750 gallons per minute. In 2004 dewatering decreased to 350 gallons per minute. All water pumped in 2003 and 2004 for dewatering purposes was pumped from trenches into an on site pond for recharge back to the Big Thompson River. In September 2004, pumping of the dewatering water into the pond ceased. All water pumped from the trenches since September 2004 has been pumped from within the slurry wall and used for the purposes described in this plan. Based on the analysis previously performed by the Applicant there are no depletions from past dewatering operations that will accrue to the river during this plan period. The depletions from evaporation and dust suppression were lagged to the stream using a Glover analysis and assuming a distance to the stream of 1,015 feet, distance to the impermeable boundary of 2,976 feet, transmissivity of 100,000 gal/day/ft and specific yield of 0.2. The depletions from well no. 60729-F (concrete production) were also lagged to the stream using a Glover analysis and assuming a distance to the stream of 1,510 feet, distance to the impermeable boundary of 2,587 feet, transmissivity of 100,000 gpd/ft and specific yield of 0.2. Replacements The proposed source of replacement for the Bernhardt pit is leased excess augmentation credits (22.50 acre-feet) available under the Town of Milliken ("Milliken") decree approved by the Division 1 Water Court in consolidated case nos. 2002CW339 and 2005CW59. The excess credits. from Milliken accrue to the Big Thompson River in the same location that the lagged depletions from the Bernhardt Pit impacts the river, therefore, no river conveyance losses will be assessed. A copy of the Lease Agreement for the Town of Milliken was submitted to this office on February 18, 2010 and a copy is attached to this letter. A monthly breakdown of depletions and replacements is shown in the attached Table No. 4 that was submitted with your report. Conditions of Approval I approve the proposed substitute water supply plan in accordance with Section 37-90- 137(11), C.R.S., subject to the following conditions: 1. This SWSP shall be valid for the period of January 1, 2010 through December 31, 2010, unless otherwise revoked, modified, or superceded by decree. If this plan will not be made absolute by a water court action by the plan's expiration date, a renewal request must be submitted to this office with the statutory fee (currently $257) by November 15, 2010.