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Mr. Brock Bowles <br />November 30, 2015 <br />Page 3 <br />2. Based on the information presented in the proposed Attachment 2.05.3(3)-28 the Pond <br />018 design details, it appears that proposed Pond 018 is incorporating a single <br />emergency spillway. Per Rule(s) 4.05.6(3)(c), 4.05.6(4), and 4.05.9(2)(a)(ii), the <br />sediment pond may be designed to provide for a single open -channel spillway, in lieu of a <br />combination ofprincipal and emergency spillways if the spillway is of non -erodible <br />construction or is earth -lined or grass -lined and designed to carry short-term infrequent <br />flows at non-erosive velocities where sustained flows are not expected. The proposed <br />Pond 018 design proposes a single earth -lined or grass -lined spillway; as such, please <br />provide information in the proposed text, pond design, or response to this adequacy <br />comment discussing the justification that the spillway as proposed is designed to carry <br />short-term infrequent flows at non-erosive velocities. <br />Response: An emergency spillway has been included to allow for a situation where a <br />storm exceeding the 100 -year 24-hour event occurs. When the 100 -year 24-hour event <br />was routed through the spillway by assuming a full pond at the beginning of the <br />demonstration, the peak velocity in the spillway was 2.41 fps. Since no flow is expected <br />in the grass -lined spillway, flow from an event exceeding a 100 -year 24-hour event <br />would be short-term, infrequent, and at non-erosive velocities. <br />Included in this package are revised materials in response to your adequacy comments <br />and a change sheet index to assist with incorporating the revised materials into the permit <br />document. If you have any questions regarding the enclosed adequacy review responses, please <br />contact Tony Tennyson at 970-824-1232 or ttennvsonLtristategt.org. <br />Sincerely, <br />4 <br />Barbara A.Walz <br />Senior Vice President <br />Policy and Compliance <br />Chief Compliance Officer <br />BAW:JS:pvt <br />Enclosures <br />AN EQUAL OPPORTUNITY/AFFIRMATIVE ACTION EMPLOYER <br />A Touchstone Energy Cooperative <br />