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• ARCO Coal Compam• <br />\ Permits and plia nce Group <br />O ~ 555 Seventeen h Street <br />' '.l ailing Address: Box 5300 <br />a Denver. Colorado 80217 <br />Telephone 303 Si 5 7500 <br />May 4, 1981 <br />Mr. Tom Gillis <br />Reclamation Specialist <br />Mined Land Reclamation <br />State of Colorado <br />1313 Sherman Street <br />Denver, Colorado 80202 <br />Dear Tom; <br />~ iiiriiiiiinriirii; <br />~i <br />Following are the responses to Jim Herrons memo of April 20, 1981, <br />regarding sediment control. <br />1. A description of the material overlying the PVC under drain <br />system for the sediment ponds must be submitted. Also, cross- <br />sections of the drainage system must be submitted. This informa- <br />tion is needed to ascertain whether effluent limitations can be <br />met if the sediment ponds contain substantial amounts of sediment. <br />The response to this question can be found in <br />Volume IV, Exhibit 3. 1.1.D, P9. 2200-5 - <br />Type 3 Material, and Volume IV, Drawing Set, <br />pg. 47 and 66, Typical Cross-Sections. <br />2. The applicant should clarify why two different drainage areas <br />were used to determine flows from the 10-year, 24-hour storm and <br />the MPF assumption "8" inflow. <br />This question has been resolved as per our <br />discussion with J. Herron on April 29, 1981. <br />3. The applicant has not included a description of the method used <br />to size the drainage ditches. Using Mannings Formula, the ditches <br />are properly sized, but the method used by the applicant should be <br />stated in the text. <br />ARCO Cml Company 1, a Ol rl,ion of Allantl[fllc M1LelO Ca mpeny <br />