2012-06-05_HYDROLOGY - M1977526 - Laserfiche WebLink

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Mr. Kathryn Cloutier Worthing SWSP June 5, 2012 Page 2 that it is appropriate to designate 28 acres of exposed ground water as being pre -81 and therefore exempt from evaporative replacement requirements. The area receiving this credit is depicted in the attached Figure 4 — Final Reclamation Map. The pre -81 credit is tied to this physical location and may not be reallocated to other areas within, or outside of, the mining boundary. Based on a February 21, 2012 aerial photograph of the site, there are 32.11 acres of exposed ground water. Subtracting the 28 acres of pre -81 areas result in 4.11 acres of post -80 exposed ground water requiring replacement of depletions from evaporation. Gross evaporation at this site is estimated to be 45 inches (3.75 feet) per year with an effective precipitation amount of 0.83 feet. This equates to an annual evaporative loss of 12.02 acre -feet for the 4.11 acres of post -80 ground water exposed at the Site. See Tables 1 and 2 for the monthly distribution of the above water uses Depletions at the Site do not hit the river instantaneously and must therefore be lagged back to the river. The Applicants engineer estimated the lagged depletions that occur due to gravel mining by using the Glover equation (Glover and Balmer, 1954). The distance between the exposed water at the pit and the stream edge is 437 feet as measured from the centroid of the lake to the perpendicular distance to the South Platte River. A transmissivity value of 100,000 gallons per day per foot was used as well as a specific yield of 0.2. For the purposes of this SWSP it was assumed that the depletions at the exposed water at the Site would occur for one year since AFS is actively backfilling the lake so that only pre -81 areas are exposed. The equation was calculated from t = 0 to t = 1.25 years. The river depletion analysis shows that the Worthing Pit's stream depletion will equal approximately 12.04 acre -feet during the approval period. The estimated monthly lagged depletions are provided in Table 2. Replacements The source of replacement water for this plan will be provided by leased fully consumable water from the City of Aurora. Aurora will deliver the water to the river as effluent from the Metro Wastewater Treatment Plant located approximately 12 miles upstream of the mining operation. As such, a transit loss of 6% (0.5% per mile) is assessed on all deliveries made by Aurora to be used at the Worthing Pit. A copy of the May 17, 2011 lease, and the May 22, 2012 amendment has been provided to this office and is attached to this letter. This lease is also shared with the neighboring Stagecoach Stop Pit and provides sufficient replacement water for Worthing Pit in 2012 with the exception of January. Therefore the duration of this SWSP approval is February 1, 2012 through December 31, 2012. See Table 3 for the monthly replacement schedule. It should be noted that delayed depletions will occur beyond December 31, 2012 and thus this SWSP will need to be renewed even if all the backfilling is complete by the end of this SWSP duration. Long Term Augmentation Requirements In accordance with the letter dated April 30, 2010 from the Colorado Division of Reclamation, Mining, and Safety ( "DRMS "), all sand and gravel mining operators must comply with the requirements of the Colorado Reclamation Act and the Mineral Rules and Regulations for the protection of water resources. Specifically gravel pit operators are required to show that they can comply with any long term augmentation requirements once mining operations are completed. The reclamation plan for the Site includes backfilling the lake so that only 28 acres remain. These 28 acres are considered pre -81 and thus no long term augmentation to cover evaporative losses will be required after reclamation is complete. AFS holds a bond through DRMS in the amount of $230,800 which can be used to complete the reclamation plan in the unlikely event the operator walks away from the Site before reclamation is complete.