2013-05-29_HYDROLOGY - M2001085 - Laserfiche WebLink

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Mr. Craig Lis Page 2 of 5 GSL Sand and Gravel SWSP March 28, 2012 depletions will occur during this SWSP approval period. All historic water use remains in the lagging analysis in order to account for any depletion still impacting the river. Previous to November 2011, the total exposed surface area at this site was 1 acre. Starting in November 2011, the operator allowed the pit to fill as mining operations were complete and the liner was not functional. The Applicant had estimated that the pit would fill with ground water to an equilibrium state within 3 months. The pit is now 26.7 acres as demonstrated by a survey of the property performed in August 2012. It is assumed the 26.7 acre pond has existed since February 2012. Net evaporative depletions were calculated using a gross annual evaporation of 45 inches from the exposed water surface, with a credit of 10.8 inches for effective precipitation. The net depletion of ground water due to evaporation of ground water exposed at the site was calculated to be 76.38 acre -feet for the period of this SWSP. The Alluvial Water Accounting System ( "AWAS ") model was used with the alluvial aquifer boundary condition option to lag depletions to the South Platte River. The following parameters were used in the model: transmissivity (T) = 63,000 gallons per day per foot, distance (X) from the surface of the exposed ground water to the river = 2,295 feet, distance (W) from the aquifer boundary through the exposed ground water to the river channel = 3,836 feet, and specific yield (SY) = 0.2. The location of the stream depletion is assumed to be perpendicular to the river. Evaporative and operational losses were considered back to January 1, 2009 because depletions during this time period may still be impacting the river. Replacements The replacement source for this plan period is fully consumable water leased from the City of Aurora ( "Aurora "). The fully consumable water will be released to the South Platte River at the outfall of the Metro Wastewater Reclamation District's Robert W. Hite treatment facility ( "Metro Sewer," WDID 0207000). Metro Sewer is located approximately 11 miles upstream of the site. As such an irrigation season transit loss of 5.5% (0.5% per mile) and a non - irrigation season transit loss of 2.8% (0.25% per mile) will be assessed on all releases. These transit losses are subject to change by the water commissioner or Division Engineer. The proposed replacement schedule is provided in Table 4. A copy of the signed lease agreement dated April 29, 2013 is attached. Long Term Depletions The final reclamation plan for DRMS Mining Permit No M- 2001 -085 had been to create a water storage reservoir through the installation of a slurry wall. The slurry wall was constructed but has not received its liner approval from DWR. Based on the Applicants statements the slurry wall leaks in multiple locations and the pit has completely filled with ground water. This is not in accordance with their DRMS permit reclamation requirements. At this time the Applicant has not decided whether to pursue repairing the liner and selling the pit as a water storage reservoir (as per their DRMS permit), to pursue an augmentation plan to cover the long term depletion requirements, or to simply backfill the pit. The current financial warranty posted for the site is $281,115. Due to the current condition of the pit DRMS has raised the warranty to $608,600 to account for backfilling of the pit. The Applicant was required to demonstrate that they are in, or are diligently pursuing, compliance with their DRMS permit and the requirements as described in the April 30, 2010 DRMS letter sent to all gravel pit operators (attached), specifically in regards to the required financial warranty at the site. The Applicant submitted to DRMS an amendment seeking to change the reclamation plan from water storage to an inert backfill operation to backfill the property to two feet above the water table. This application is pending approval and satisfies the requirement that the Applicant is diligently pursuing compliance with their DRMS permit and the requirements as described in the April 30, 2010 letter. With the next