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~ III IIIIIIIIIIIIIIII <br />• <br />September 3. 1981 <br />Mr. Larry H. O'Brian <br />Enviro~ent, Inc. <br />9999 Weat 60th Avenue <br />Arvada. Colorado 80004 <br />RE: ROBCO's Chieftain South Mine <br />Our File 581-145 <br />Dear Mr. O'Brian <br />Thank you for your letter of August 19, 1981, which adequately addressed most <br />of the staff's concerns. However, a few items require further clarificntion <br />and discussion. <br />Pltniag Plan <br />• 1) Based on the information supplied, the staff is in agreement <br />with the operator that in this particular case the benefit- <br />cost relationship does not v~arrant the separate salvage and <br />stockpiling of the B-soil horizon. <br />2) What vTill the gradient of the drainage area beT The staff <br />would like assurance that no significant ponding will occur <br />in the drainage area. Significant ponding being any large <br />volume of water which has the potential of being suddenly <br />released, thereby causing damage downhill. This concern vTas <br />fire[ expressed during Lalewood's review of the original <br />application. <br />3) How often will the settling pond be cleaned? <br />4) Will there be any discharge from the sattling pond during the <br />mining phase of this operation? If so, how will this discharge <br />be controlled? <br />S) Wtiat criteria (10 year event, 100 year event, etc.) hae the <br />settling pond and drainage area been designed for? <br />Exhibit E - Reclamation plan <br />. 1) For the reasons outlined in my letter of August 10, 1981, the <br />staff still suggest that ROBCO leave 4:1 slopes rather than <br />2:1 slopes wherever possible. However, based on your professional <br />judgement that the 2:1 slopes will be stable and capable of <br />sustaining vegetation. sad the fact that it will be ROBCO's <br />reapoasibility to see that this is indeed the case; the staff <br />