2014-01-09_HYDROLOGY - M2011049 - Laserfiche WebLink

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Partners Combined SWSP December 30, 2013 Depletions Page 2 of 5 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 as a result of open mining of sand and gravel ( "pre -81 areas "), regardless of whether mining continued after December 31, 1980. Per our "General Guidelines for Substitute Water Supply Plans for Sand and Gravel Pits" updated April 1, 2011, pre -81 areas are tied to the physical location at which the groundwater was exposed prior to January 1, 1981 with the exception for areas whose reallocation was approved by the State Engineer prior to January 1, 2011. Previous SWSPs (prior to January 1, 2011) approved the pre -81 area without specific mention of its location. Therefore, the State Engineer's Office allowed the pre -81 area to be re- allocated and memorialized under the May 11, 2011 SWSP approval. The applicant provided a map (Figure 1 — Home Office Pit) showing the specific location of the pre -81 area, which includes the 22.1 acres of ground water exposed in Lamb Lake A. The credits for the pre -81 area are tied to the location identified on Figure 1 — Home Office Pit and may not be re- allocated to other areas of ground water exposure within the gravel pit boundary. Evaporative depletions for the remaining lakes were calculated using a gross annual evaporation of 38 inches, with a credit of 10.58 inches for effective precipitation (based on an average annual precipitation of 15.12 inches for the Fort Collins weather station). You have estimated the surface area of Treiber Lake B as 25.6 acres which results in a net evaporative depletion of 58.49 acre - feet for this plan period. You have estimated the surface area of ground water exposed in the Lamb Lakes after December 31, 1980 as 61.8 acres which results in a net evaporative depletion of 141.19 for this plan period. You have assumed that no ground water was exposed in Treiber Lake A after construction of the slurry wall in August, 2013. Lagged depletions resulting from exposure of ground water in Treiber A Lake prior to August of 2013 will continue to be replaced under this SWSP. The construction of a slurry wall around Treiber Lake B will require approximately 20 acre -feet of water which will be consumed in mixing the bentonite slurry mix. You have estimated that 5 acre - feet will be required for this purpose in June 2015, 10 acre -feet in July 2015, and 5 acre -feet in August 2015. This water will be pumped from Treiber Lake B and is considered to be 100% consumed. The monthly evaporative depletions to the Cache la Poudre River were lagged using the AWAS program developed by the IDS Group at Colorado State University. The parameters used in the model were an average distance from the centroid of each lake to the river (X) of 744 feet, an estimated distance from the site to the no flow aquifer boundary (W, measured perpendicular to the point of impact) of 6,500 feet, an aquifer transmissivity (T) of 160,000 gallons per day per foot, and a specific yield (S) of 0.2. Since the water required for slurry wall construction will be pumped from Treiber Lake B, those depletions were lagged using a distance (X) of 640 feet from the centroid of Treiber Lake B to the river. All other parameters remained the same. Lagged depletions due to past and projected evaporation and operations at the site will total 202.9 acre -feet for 2014 and 218.7 acre -feet for 2015. Should the slurry wall around Treiber Lake A not pass the leak test as contemplated in this SWSP, an amended SWSP must be submitted to this office. Replacements The first source of replacements under this SWSP is reusable municipal return flows from the East Larimer County Water District (ELCO). ELCO is one of the Tri- Districts. ELCO recently decreed its municipal return flows in Case No. 09CW282 on June 29, 2012. Their accounting was approved by the Division Office on August 23, 2012. The reusable municipal return flows accrue to the Poudre River primarily at either the Fort Collins Waste Water Treatment Plants Nos. 1 & 2 (WDIDs 0302313 and 0302314, respectively) or the Boxelder Sanitation District Waste Water Treatment Plant (WDID 0302322).