2013-04-11_HYDROLOGY - M1980149 - Laserfiche WebLink

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Ms. Michelle L. Hatcher Hokestra SWSP April 10, 2013 Page 3 of 9 However, in accordance with water court case 09CW49 and current administrative policy found in the State Engineer's General Guidelines for Substitute Water Supply Plans for Sand and Gravel Pits (updated April 2, 2011), the State Engineer will (1) not require replacement for evaporation on pre -81 areas regardless if mining continued at the site post 1980 and (2) the pre -81 area is limited to the location where it existed prior to 1981 unless the Applicant can show that the State Engineer previously recognized in writing a re- allocation of the pre -81 areas within the permit boundaries. Previous SWSPs (prior to 2009) recognized a pre -81 area of 14.1 acres and the Applicant was not required to replace evaporative depletions for 14.1 acres of exposed surface area regardless of where within the permit boundary water was exposed. Since the Applicant was previously allowed to reallocate 14.1 acres of pre -81 area, the State Engineer's Office will allow the 14.1 acres of pre -81 area to be set at a location other than the location of the original pre -81 exposure. The Applicant is only claiming 14.1 acres of pre -81 area under this SWSP. The area to receive the pre -81 credit is shown on the attached "Revised Figure 1" dated March 5, 2012. The exemption from augmentation requirements for the pre -1981 area is tied to the physical location identified on this figure and may not be applied to other areas of ground water exposure within the gravel pit permit boundaries. Net evaporative depletions were calculated using a gross annual evaporation of 40 inches from the exposed water surface, with a credit of 9.38 inches for effective precipitation. No phreatophyte credit has been applied to this plan. The net depletion of ground water due to evaporation from the 56.4 acres of ground water exposed at the site after December 31, 1980 was calculated to be 88.8 acre -feet. This assumes that Cells 5 & 6 do not expose any ground water after April 2013 due to dewatering activities. See Table 13 for a monthly breakdown of evaporative depletions at the site Weld County uses ground water from the southwestern reclaimed cell (Cell 1) to irrigate landscape at the Weld County Southwest Service Center. Weld County conducted a field survey on February 7, 2008 and reported that the landscaped area consists of 0.15 acres of blue grass and 5.5 acres of native grass. This area will be irrigated using water pumped from Cell 1 during the growing season of April through October. According to a Modified Blaney - Criddle analysis, the potential crop consumptive use for the 0.15 acres of blue grass is 0.30 acre -feet, and the potential crop consumptive use for the 5.5 acres of native grass is 9.4 acre -feet. Since the irrigation occurs directly around the reclaimed cell, the plan assumes that irrigation return flows will return to the river in the same timing as the depletions. The total consumptive use of ground water associated with the Hokestra Pit is estimated to be 98.4 acre -feet, consisting of evaporation loss from 56.4 acres of post -80 exposed surface area and water used for irrigation at the SWSC.