2012-03-14_HYDROLOGY - M1978210 - Laserfiche WebLink

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Ms. Michelle L. Hatcher Geisert SWSP March 14, 2012 Page2of5 with product or dust control. On site activities will include performing the liner test for Cells 3 and 4. Other than evaporation from exposed ground water surface areas, dewatering operations will be the only source of depletions at the site. During the period of this plan, the County anticipates the total exposed surface area will be approximately 13.7 acres. According to the information submitted, 4.4 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 infrared photo taken in June 1980 (See Figure A -3). The previous SWSP only recognized 4.1 acres as qualifying for the pre -81 credit. 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 6 acres and the Applicant was not required to replace evaporative depletions for 6 acres of exposed surface area regardless of where within the permit boundary water was exposed. Since the Applicant was previously allowed to reallocate the pre -81 area, the State Engineer's Office will allow the pre -81 area to be set at a location other than the location of the original pre -81 exposure. Under the March 7, 2011 SWSP approval the location of the pre -81 area was permanently set to that location shown on Figure 1 of the March 7, 2011 SWSP. Since the Applicant has provided convincing evidence of a larger pre -81 exposure the previously allocated area is being corrected. The area to receive the pre -81 credit is shown on the attached "Revised Figure 1" dated March 5, 2012. The exception to the requirement to replace evaporative depletions for the pre -1981 area is now tied to the location identified on this figure and may not be applied to other areas of ground water exposure within the gravel pit permit boundary. Net evaporative depletions were calculated using a gross annual evaporation of 45 inches from the exposed water surface, with a credit of 9.87 inches for effective precipitation. As dewatering operations are projected to begin April 1, 2012 with the bulk of the dewatering completed by the end of the month, the April evaporation assessed on cells 3 and 4 was estimated based on an average surface area derived from the beginning surface area and dewatered surface area. The representative Cell 3 and 4 surface area was found to be 21.7 post -1980 acres. For May through September, the evaporative losses were applied assuming the site was in a fully dewatered condition for Cells 3 and 4 with a surface area of 4.5 post -1980 acres. After September 2012 it is assumed the liner for Cell's 3 and 4 would be approved and thus no evaporation was charged for any location within the liner boundary. Cells 1 and 2 are expected to remain at 4.8 post -80 acres for the entire duration of this SWSP approval period. No phreatophyte credit has been applied to this plan. The net depletion of ground water due to evaporation from ground water exposed at the site after December 31, 1980 is 26.4 acre -feet. Dewatering is projected to occur at a continuous rate of 4,000 gallons per minute in April 2012, be reduced to 2,000 gallons per minute in May 2012, and then be reduced further to 50 gallons per minute during the leak test to occur June 2012 through September 2012. The purpose of the dewatering operation is to allow for the slurry wall leak test for Cells 3 and 4. It is projected that dewatering operations will cease after September 2012 after which the Operator plans to have received approval of the liner. These estimated dewatering values are accepted for the purposes of estimating and projecting water needs at the pit however, all dewatering operations must have a totalizing flow meter installed to accurately record the monthly