2015-03-11_HYDROLOGY - M1998013 - Laserfiche WebLink

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Mr. Andy Rodriguez, P.E Shores Pit SWSP March 9, 2015 Page 2 of 5 In accordance with the letter dated April 30, 2010 (copy attached) 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. The April 30, 2010 letter from DRMS requires that you provide information to DRMS to demonstrate you can replace long term injurious stream depletions that result from mining related exposure of ground water. The DRMS letter identifies four approaches to satisfy this requirement. In accordance with approach nos. 1 and 3, you have obtained a bond for $888,677.00 through DRMS for lining or backfilling of the exposed ground water. This is a reduction from the previous bond, which is based on the approval of the four lined reservoirs Depletions Currently 11 acres of ground water surface is exposed at the Shores Pit within the silt pond. It is estimated that starting in May 2015 an additional 1.5 acres will be exposed in the dewatering trenches at the Burch property. The net depletion of ground water due to evaporation from these 11 acres is calculated to be 28.82 acre -feet for this plan period. Also the net depletions due to the evaporation from the 1.5 acres exposed in the dewatering trenches is calculated to be 3.16 acre -feet from May through December 2015. Net evaporative depletions were calculated using a gross annual evaporation of 42 inches from the exposed water surface, with an annual credit of 10.56 inches for effective precipitation. The applicant has not requested ice cover credit under this plan. Ground water from the 11 acre silt pond is used for dust control and concrete batching. The Applicant estimates that 1.66 acre -feet of water per year will be used for dust control. Approximately 105,000 cubic yards of concrete will be batched onsite during this plan period at a depletion of 40 gallons per cubic yard, resulting in a water requirement of 12.89 acre -feet. However the plant utilizes a water tap for the concrete batching at a rate of 4 million gallons per year, or 12.27 acre -feet during this plan period. Therefore the resulting annual net depletion from concrete batching is 1.64 acre -feet. The water supplied by Central Weld shall be metered along with the total water used for onsite concrete batching to aid in calculating the actual depletions owed. The data from both metered sources shall be included in the accounting provided to the Division Engineer. The Applicant also anticipates that 505,000 tons of aggregate will be mined during this plan period. Approximately 58,670 tons of aggregates are mined within the slurry wall area of Cell D in January and February 2015 therefore there are zero depletions associated with the mined material for these two months. Starting in March 2015 the aggregate production will occur at the Burch property therefore the associated depletions from March through December 2015 will be 13.14 acre -feet from 446,330 tons of mined material. The net evaporation and operation depletions associated with the Shores pit are estimated to be 49.53 acre -feet, as shown in the attached Table 4. Dewatering of the site commenced in February 1999 at a rate of 300 gallons per minute and had remained constant during mining of cells A, B, C, and D. For modeling purposes dewatering was stopped on December 2006 which is the year the slurry walls for the three cells were completed. As long as dewatering operations in cell D remain constant, it is assumed that the accretion credits are sufficient to offset any.lagged depletions as this water is not used and immediately returns to the stream. In addition dewatering from the Burch property will be run at a rate of 300 gallons per minute starting in May 2015. The dewatering from the Burch property will be recharged in the north site and returned back to the Saint Vrain River. The SWSP accounts for the net depletions at the river that occur due to the past