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0 <br />Mr. Zach Trujillo <br />March 3, 2017 <br />Page 3 <br />• Exhibit 7-23, Figure D4 - Facility Access Road Western Portion <br />• Exhibit 7-23, Figure DS -Jubb Creek Access Road <br />Response: A table has been added to Map 25 Sheet 4, which provides further information on the cut <br />slopes by station to demonstrate compliance with Rule 4.03.1(3)(d). <br />Exhibit 7-23 Figures D 1 - D5 have not been updated. However, text has been provided in Exhibit 7, <br />Item 23, Part 7, which provides information on the cut slopes that may be encountered during the <br />construction of the access roads. <br />Finally in 2016, Colowyo conducted a geotechnical drilling program to obtain and analyze soil, <br />weathered rock, and unweathered rock samples along the Collom Haul Road. Due to the expected <br />life of the Collom Haul Road a conservative approach was used for rock cut slope design for <br />sandstones and shales with a safety factor of 1.5 (in accordance with 4.03.1(3)(d)(i)). Weathered <br />rock that is cut to an unweathered rock surface will soften over a long period of time. Therefore, the <br />residual or "reduced" shear strength was used for rock cut slope design. Reduced strength <br />parameters are intended to reflect long-term strength conditions. <br />8. In Exhibit 7, Item 23, Part J- Sediment Control System for the Initial Facililies Disturbance Area, it is <br />stated that "[6111 undisturbed areas are modeled at a curve number of 57... based on Volume 25, <br />Exhibit 7, Table 1 values. " Reviewing Volume 25, Exhibit 7, Table 1 values, the curve number 57 is <br />associated with cover type - Oak/Aspen. For the associated areas in Exhibit 7, Item 23, Part J, it <br />appears to the Division sagebrush is the dominant cover type, when comparing to the approved Map <br />4C Sheet 6 of 11. According to Volume 25, Exhibit 7, Table 1 values, sagebrush is associated with <br />the curve numbers 47 or 63 depending on hydrologic condition and percent cover. Please provide the <br />Division a reason for the use of c urve number 57 in Exhibit 7, Item 23, Part J - Sediment Control <br />System for the Initial Facilities Disturbance Area or a revised hydrologic model using a corrected <br />curve number. <br />Response: The SEDCAD model for Exhibit 7, Item 23, Part J has been updated with the curve <br />number of 63 as indicated by the Division. Also, Exh. 7-23, Figure J1 has been updated with the <br />corrected curve number. <br />9. It appears to be a text error in Exhibit 7, Item 23, Part J- Sediment Control System for the Initial <br />Facilities Disturbance Area. On page &h. 7-23J-2, paragraph five, & states the third SECAD model <br />was ran for a 25 year, 25 hour storm event while the model was ran for a 25 year, 24 hour storm <br />event. Please provide a corrected page &h. 7-23J-2. <br />Response: The typographical error on Page Exh. 7-23J-2 has been corrected as requested. <br />10. When reviewing Exhibit 7, Item 23, Part K- Sediment Control System for the Temporary Facilities <br />Pond that the curve number 57 was used for all undisturbed (refer to comment 8 for additional curve <br />number comments). Again, when comparing to the approved Map 4C, the area appears to be mainly <br />sagebrush which is associated with curve numbers 47 or 63. Please provide the Division a reason <br />AN EQUAL OPPORTUNITY / AFFIRMATIVE ACTION EMPLOYER <br />A Touchstone Energy' Cooperative <br />