2012-08-01_HYDROLOGY - M1980149 - Laserfiche WebLink

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Ms. Michelle L. Hatcher Hokestra SWSP July 30, 2012 Page 2 of 7 this plan period. The 9.9 -acre cell (Cell 3) has been backfilled, eliminating any exposed surface area within that cell. The remaining cells have been reclaimed. According to the information provided by the applicant, the County will continue to dewater the 35.0 -acre cell (Cell 2) during this plan period. The County intends to line this cell, but lining has been delayed and the cell will continue to be dewatered until lining is complete. The surface area of the dewatering trench and collection pond for this cell total 0.37 acres. As long as the pit is continuously dewatered, the water returned to the stream system should be adequate to offset the depletions. For administration and to determine post - pumping depletions after dewatering has ceased, or is reduced, a totalizing flow meter must be installed to accurately measure the monthly dewatering volumes. If not already in place, this SWSP will not be renewed until such a meter is installed at the site. Currently 70.5 acres of exposed ground water surface area is exposed at the Hokestra Pit site. According to the submitted information, a total of 15.0 acres of ground water surface was exposed to the atmosphere within the reclamation permit boundary prior to January 1, 1981 ("pre-81"), as evidenced from an aerial photo taken in September 1981 (See Figure A -3). The previous SWSP only recognized 3.6 acres as qualifying for the pre -81 credit as a portion of the 15.0 was no longer exposed. 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 now 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 143.9 acre -feet.