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Gary Isaac <br />CAM-Colorado, LLC <br />August 29, 2008 <br />Page 17 <br />43. The hydrology designs found in Volume IV use 1.4 inches as the 10 year-24 hour <br />precipitation event, 1.8 inches as the 25 year-24 hour event and 2.2 inches as the 100 <br />year-24 hour event. However, examination of the 1973 NOAA Atlas "Precipitation - <br />Frequency Atlas of the Western United States" shows larger precipitation values. The <br />NOAA Atlas values are about 1.7 inches, 2.05 inches and 2.6 inches respectively. Also, <br />the hydrology designs for the McClane Mine just to the north used 1.7 inches as the 10 <br />year-24 hour precipitation event. Please explain CAM's values or revise the Sedcad <br />designs appropriately. <br />44. There are several examples of soil types shown on Map-04 not coinciding with soil types <br />used in the curve number determinations in Volume IV for the various drainage areas. <br />Most of the differences do not have an effect on the curve number determination but, in <br />order to avoid any future confusion, the Division believes appropriate changes should be <br />made. <br />A. In the Sedcad design for pond A, on pages A-3, A-4 and A-5, soil types of loam, <br />Persayo Sandy Loam and Avalon Sandy Loam are used. However, examination of <br />Map-04, "Soils", shows that there are only rock outcrops in the area draining to <br />pond A. Please explain the use of these soil types in the hydrology designs or <br />make changes to the Sedcad designs to reflect the soils on Map 04. <br />B. Concerning pond G, on page G-3 of Volume III, a soil type of Persayo Sandy <br />Loam is used for the salt desert shrub curve number determination. However, <br />referring to Map-04, Soils, there does not appear to be any such soil type in the <br />drainage area for pond G. Please explain the use of these soil types in the <br />hydrology designs or make changes to the Sedcad designs to reflect the soils on <br />Map 04. <br />C. In the hydrology designs for pond G on pages G-3 and G-4, there are no soil types <br />of torriorthents, Chipeta Silty Clay or rock outcrop used for any of the curve <br />number determinations, even though those soil types appear in the pond G <br />drainage on Map-04. Please explain the use of these soil types in the hydrology <br />designs or make changes to the Sedcad designs to reflect the soils on Map 04. <br />D. In the hydrology designs for pond C on pages C-3, C-4 and C-5, the soil types <br />used in the curve number determinations do not appear to match the soil types <br />shown on Map-04 for the pond C drainage area. In one case, the soil type is listed <br />as being Persayo Sandy Loam but there does not appear to be any such soil type <br />shown on Map-04 for the pond C drainage area. Also, soil types of Chipeta Silty <br />Clay, Chipeta Clay, torriorthents and Aga Very Gravelly Loam appear on Map-04 <br />within the pond C drainage but do not appear in any of the curve number <br />determinations for pond C. Please explain the use of these soil types in the