2015-03-11_HYDROLOGY - M1998013 - Laserfiche WebLink

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Mr. Andy Rodriguez, P.E Shores Pit SWSP March 9, 2015 Page 3 of 5 dewatering operations (February 1999 through December 2006) and the proposed dewatering operations estimated to start in May 2015. Lagged depletions from past and current dewatering at the site during the period of this plan total 11.86 acre -feet. The depletions from evaporation, water removed in the mined product, dust suppression, concrete batching and dewatering were lagged to Saint Vrain Creek using a Glover analysis. The following parameters were used in the model to lag operational and evaporative losses: transmissivity (T) = 72,300 gallons per day per foot, specific yield (SY) = 0.2, the location from the parallel impermeable boundary to the creek (W) = 10,000 feet, and the distance from the exposed ground water in the silt pond to the creek (X) = 5,409 feet for the period of 1998 -2007 and (X) = 6,488 feet for the period of 2008 -2015 (due to the slurry wall approvals). For the dewatering water for the period of 1998 through 2006 a distance (X) =4,507 feet was used and for the mined product from March through December and evaporation from the dewatering trenches from May through December 2015 a distance (X) _ 3,062 was used. The attached Table 4 provides a monthly schedule of lagged depletions to the river system due to operational losses, shown to be 49.53 acre -feet for this plan period. Including depletions due to past and current dewatering activities, the total lagged depletion to the river system in this plan period is 37.67 acre -feet, as shown on Table 4. Replacements The proposed source of replacement for the Shores pit is a lease of 33.01 acre -feet of excess augmentation credits available to Central Colorado Water Conservancy District ( "Central ") (WDID 0203334). Please note that the lease amount is for less than the calculated -depletions due to free river conditions in January 2015, during which no replacements were required to be made. The replacement water will be measured and delivered from the Shores facility adjacent to the subject site. Specifically, the water is measured as it moves through Centrals pump system and reported as a release from Shores Lakes (0503900) with the water returning to the river via the Rural Ditch Augmentation Return (0502303). A copy of the Lease Agreement with Central was submitted to this office on February 18, 2015, and is attached to this letter. A monthly breakdown of depletions and replacement is shown on the attached Table 5. Conditions of Approval I approve the proposed substitute water supply plan in accordance with Section 37 -90- 137(11), G.R.S., subject to the following conditions: 1. This SWSP shall be valid for the period of January 1, 2015 through December 31, 2015, unless otherwise revoked, modified, or superseded 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 1, 2015. 2. Well permit no. 61716 -F was obtained for the current use and exposed pond surface area of the gravel pit in accordance with 937 -90- 137(2) and (11), C.R.S. 3. The total surface area of the groundwater exposed at the Shores Pit must not exceed 11 acres in the silt pond and 1.5 acres in the dewatering trenches during the approval period - of this SWSP resulting in an annual evaporative loss of 28.82 acre -feet for the 11 acre pond and 3.17 acre -feet for the dewatering trenches. 4. The annual amount of water used at the operation shall not exceed 1.66 acre -feet for dust control, the amount used for concrete batching shall not exceed 1.64 acre -feet