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<br />4.1.1 Evaporative Depletions <br />Evaporative losses from the Timnath Pit were estimated according to guidelines outlined in <br />Paragraph 6 of the; General Guidelines for Substitute Water Supply Plans for Sand and Gravel Pits <br />Submitted to the State Engineer Pursuant to SB 89-120 & SB 93-260 (Guidelines). The gross <br />evaporation was e~~timated from the evaporation atlases in NOAA Technical Report NWS 33. Gross <br />evaporation in cel7tral Larimer County is 40 inches -per year. The gross evaporation value was <br />distributed on a monthly basis as prescribed by the Guidelines. Net evaporation from the pit was <br />calculated as the gross evaporation minus the effective precipitation in the area. Effective <br />precipitation was defined as 70% of the precipitation measured at the NOAA Fort Collins weather <br />station. The annual mean precipitation for the study period was 14.7 inches per year. For this <br />analysis, the area ~~f exposed ground water surface was estimated from observation as 25% of the <br />total area of Phase lA of the Timnath Pit mining (76.5 acres) or 19.1 acres. This area exceeds the <br />area of water surface currently exposed, but is representative of the maximum water surface that may <br />be exposed during mining operations. The mining practices being used at the Timnath Pit are aimed <br />at minimizing the amount of exposed ground water; so far they have continually limited ground <br />water exposure to an estimated 25 % of the pit area. Figure 4.1 shows the extent of current and <br />planned mining operations at the Timnath Pit. After reaching the greatest extent of open mine the <br />Timnath Pit will lose a maximum of 47.3 AF annually to evaporation from 19.1 acres of exposed <br />ground water. <br />4.1.2. OpE~rational Depletions <br />0 <br />According l.o Paragraph 7 of the Guidelines, 4% of the mined product by weight is water. A <br />maximum of 200,000 tons of material is removed from the pit each year. From experience, the rate <br />of removal of material will correspond-with the rise and fall of construction season, which picks up <br />in the spring and peaks in the summer months. The 200,000 tons were distributed to each month in <br />the operating season in a manner that seemed to reasonably correspond with construction material <br />demand. The amoL~nt of water removed from the pit each month was calculated from the distribution <br />based upon the 4% assumption resulting in an annual total of 5.9 AF. <br />Dust control operations involve the application of water pumped from the pit to the haul <br />roads. Water exposed in the pit is pumped into a water truck that periodically makes a circuit around <br />the roads in the pit to wet the area and prevent excessive suspended dust. Dust control operations are <br />only performed as often as necessary to keep the dust down and will vary from day to day depending <br />on the weather and the traffic in the pit. During peals season, from May to September, when the <br />C:\Projects\CODKCOI\Admin\DKC 2006 SWSP Application.doc 10 Scott Water Engineers, LLC <br />