2015-05-19_HYDROLOGY - M1977526 - Laserfiche WebLink

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Mr. Branden Effland Worthing SWSP May 13, 2015 Page 2 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. In 2014, AFS backfilled 3.38 acres of the 4.11 acres of post -80 exposed groundwater. This SWSP will cover depletions related to the evaporation off the remaining 0.73 acres of post -80 exposed groundwater through May of 2015, at which point the remaining acreage will be backfilled. 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 evaporative loss of 0.64 acre-feet for the 0.73 acres of post -80 ground water exposed at the Site through May of 2015. See Tables 1 and 2 for the monthly distribution of the above water uses 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) = 100,000 gallons per day per foot, distance (X) from the centroid of the surface of the exposed ground water to the river = 437 feet, distance (W) from the aquifer boundary through the exposed ground water to the river channel = 19,000 feet, and specific yield (SY) = 0.2. The location of the stream depletion is assumed to be perpendicular to the river. The lagged depletions due to evaporation and mining operations total 1.96 acre-feet for this SWSP period are shown in Table 4. So long as all diversions for dust suppression cease and exposed acreage is backfilled by May 31, 2015, no lagged depletions will occur after this SWSP period. Replacements The source of replacement water for this plan will be provided by leased fully consumable water from the City of Aurora. On a daily basis, Aurora will deliver the water to the river as effluent from the Metro Wastewater Treatment Plant (WDID 0200700) located approximately 12 miles upstream of the mining operation. A transit loss of 6% (0.5% per mile) is currently assessed on all deliveries made by Aurora to be used at the Worthing Pit; however the rate of transit loss is subject to change. A copy of the May 17, 2011 lease and a October 8, 2014 E-mail from Aurora Water confirming the 2015 replacement schedule has been provided to this office and is attached to this letter. See Table 5 for the monthly replacement schedule. So long as the remaining exposed area is backfilled by May 31, 2015, depletions will not occur beyond December 31, 2015 and future SWSPs will not be needed. 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.