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Mr. Andy Rodriguez, P.E. <br />April 21, 2011 <br />Page 2 of 5 <br />In accordance with the letter dated April 30, 2010 (copy attached) from the <br />Colorado Division of Reclamation, Mining, and Safety ("DRMS"), all sand and gravel <br />mining operators must comply with the requirements of the Colorado Reclamation Act <br />and the Mineral Rules and Regulations for the protection of water resources. The April <br />30, 2010 letter from DRMS requires that you provide information to DRMS to demonstrate <br />you can replace long term injurious stream depletions that result from mining related <br />exposure of ground water. The DRMS letter identifies four approaches to satisfy this <br />requirement. In accordance with approach nos. 1 and 3, you have obtained a bond for <br />$1,045,840 through DRMS for lining or ba'ckfilling of the exposed ground water. <br />Depletions <br />Currently 4.6 acres of ground water surface is exposed at the Shores Pit within the'silt <br />pond (4 acres) and the dewatering trenches ?(0.6 acres). The net depletion of ground water due <br />to evaporation from the 4.6 acres of ground water exposed at the site was calculated to be <br />12.32 acre-feet. Net evaporative depletions were calculated using a gross annual evaporation of <br />37.5 inches from the exposed water surface;,, with a credit of 10.56 inches for effective <br />precipitation. Computation of evaporation under this plan was also reduced during the ice <br />covered period. You have assumed the ice covered period to occur during the months of <br />January and December, based on the average temperatures of 26.99°F for January and <br />28.62°F for December; taken from the Longmont 2ESE weather station. However, for the <br />purpose of this SWSP, the Applicant shall replace the net evaporation depletions from the <br />exposed ground water surface area that may occur during the assumed ice covered period (the <br />months of January and December) for any time that the water surface is not completely covered <br />by ice. <br />Computation of the net evaporation during any time that the water surface is not <br />completely covered by ice shall be determined as the pro-rata amount of the monthly gross <br />evaporation rate distribution amount identified in the State Engineer's General Guidelines for <br />Substitute Supply Plans for Sand and Gravel Pits, subtracting the pro-rata amount of the <br />effective precipitation for that period. <br />Ground water from the 4 acre silt pond is used for washing aggregate, dust control and <br />concrete batching. Hall-Irwin anticipates that1700,000 tons of aggregate will be mined during this <br />plan period. The material is mined below the ground water table and is washed; therefore the <br />water retained in the mined product is considered to be 4.0% of the mined material by weight, <br />equal to 20.59 acre-feet. Hall-Irwin estimates that 3.33 acre-feet of water per year will be used <br />for dust control. Approximately 85,000 cubici yards of concrete will be batched onsite at a <br />depletion of 40 gallons per cubic yard, resulting in an annual depletion of 10.43 acre-feet. <br />The net evaporation and operation depletions associated with the Shores pit are <br />estimated to be 46.66 acre-feet, consisting of 12.32 acre-feet of evaporation loss from 4.6 acres <br />of exposed surface area, 20.59 acre-feet removed with the mined product, 3.33 acre-feet for on- <br />site dust control, and 10.43 acre-feet used for concrete batching, as shown in the attached <br />Table 2. <br />Dewatering of the site commenced in October 1998 at a rate of 300 gallons per minute <br />and continued through December 2007. Dewatering at the site (cell D) began again in January <br />2010 and will continue through December 2011. The SWSP accounts for the net accretions <br />credits at the river that occur due to the dewatering operation at the site and for the depletions