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Hydrologic Soil Grouo <br />. As per the SEDCAD Version 3 Training Guide, page 5-16, <br />"The SCS has classified greater than 4,000 <br />soil series into the four HSG's according to <br />their minimum infiltration rates for <br />approximate saturated bare soil conditions". <br />It is important to note that Colorado State University (CSU) <br />performed a study entitled Hydrologic and Erosional Characteristics <br />of Regraded Surface Coal Mined Land in Colorado, of which Colowyo <br />was a participant. The study was funded by the Office of Surface <br />Mining (OSM). This report is included in its entirety in the <br />Colowyo permit, Exhibit 7, item 9. <br />Since the definition of a HSG is dependant upon the <br />infiltration rate, please note Table 10, page 58 of the CSU study, <br />which shows that out of all coal mines tested, the infiltration <br />rate at Colowyo was the highest at 1.87 inches per hour. <br />Going back to the SCS definition of a HSG and referring also <br />to Table 5.1, page 5-16, SEDCAD Training Guide, even if the Colowyo <br />infiltration rate of 1.87 inches per hour was reduced to one <br />quarter of its value, the HSG for reclaimed land at Colowyo could <br />be classified as HSG A with low runoff uotential. <br />_• Additionally, as per the SEDCAD Version 3 Training Guide, page <br />5-16, <br />"In selecting a HSG classification, <br />consideration should be given to the influence <br />of heavy equipment..." and "earth moving <br />equipment may significantly compact a soil <br />layer resulting in reduced infiltration and an <br />increase in the HSG letter designation; e.g. B <br />to a C". <br />In discussing this matter with Dr. Warner, he stated that the <br />converse is also true. Reclamation practices can serve to reduce <br />soil compaction resulting in increased infiltration and a decrease <br />in the HSG letter designation, e.g. C to a B. <br />The exceptional infiltration rates found at Colowyo can be <br />explained by the standard reclamation practices of chisel plowing <br />to prevent soil compaction, contour furrowing, range land seed <br />drilling, and terracing. <br />• <br />