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COMMENT RESPONSE DOCUMENT FOR TR-73 <br />FOR MARCH 16, 2009 COMMENTS <br />Response Accepted. <br />2. The Division does not agree with some of the SCS curve number ranges as presented in Table 1 <br />(Exhibit 7, page 3) for the following two reasons. <br />a. Hydrologic soil groups are represented in Table 1 as B soils for all reclaimed lands (topsoiled <br />areas post-reclamation). According to information provided on page 4, Exhibit 7, the Campass, <br />Burnette, and Work Series soils are the three dominant soils within the proposed disturbed area. <br />The Burnette and Work series are C soils (reference TR-55, Second Edition, June 1985, Exhibit <br />A-1, Hydrologic soil groups for US soils). Given that soils will likely experience some <br />compaction during re-application, representing all soils as being in the C category would likely <br />result in more accurate storm runoff modeling. Please use accurate soils information. <br />b. No site-specific evidence in the form of vegetation sampling results for total cover was <br />provided to justify 85% cover on areas of 1-2 years growth or the 3+ year growth areas. Please <br />provide support for the amount of hydrologic cover based on the annual vegetation surveys of <br />the reclaimed area. <br />Response: Documents are available from the NRCS website showing the county-wide <br />mapping reports that have been done for both Rio Blanco and Moffat <br />counties. Each unique mapping unit has been assigned a hydrologic soil <br />group. <br />The following text discussion was obtained from the Moffat County NRCS report, <br />with bold text added for emphasis: <br />Hydrologic soil groups are based on estimates of runoff potential. Soils are assigned to one of four <br />groups according to the rate of water infiltration when the soils are not protected by vegetation, are <br />thoroughly wet, and receive precipitation from long duration storms. The four hydrologic soil groups <br />are: <br />Group A. Soils having a high infiltration rate (low runoff potential) when thoroughly wet. These consist <br />mainly of deep, well drained to excessively drained <br />sands or gravelly sands. These soils have a high rate of water transmission. <br />Group B. Soils having a moderate infiltration rate when thoroughly wet. These consist chiefly of <br />moderately deep or deep, moderately well drained or well drained soils that have moderately fine texture <br />to moderately coarse texture. These soils have a moderate rate of water transmission. <br />Group C. Soils having a slow infiltration rate when thoroughly wet. These consist chiefly of soils having <br />a layer that impedes the downward movement of water or soils of moderately fine texture or fine texture. <br />These soils have a slow rate of water transmission. <br />Group D. Soils having a very slow it}filtration rate (high runoff potential) when thoroughly wet. These <br />consist chiefly of clays that have a high shrink-swell potential, soils that have a high water table, soils <br />that have a claypan or clay layer at or near the surface, and soils that are shallow over nearly impervious <br />material. These soils have a very slow rate of water transmission. <br />If a soil is assigned to a dual hydrologic group (A/D. BID, or CID), the first letter is for drained areas <br />and the second is for undrained areas.