2004-10-22_REVISION - M1988037 - Laserfiche WebLink

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ocr Z s 2004 Greg Lewicki And Associattes O(visian of Minerals end Geology 11541 Warriagtoa Court Parker, CO USA 80138 Russ Means DMG Grand Junction Field Office 101 South 3`s Street, Room 301 Grand Junction, CO 81501 Dear Mr. Means, September 20, 2004 This letter is in response to the 8/30/04 inspection sent to Brent: Kerr of United Companies regarding the Norwood Gravel Permit No. M-1988-037. Three problems were noted on the site. United mines using near vertical highwalls. In older pits which United has acquired, this tends to differ from the permitted mining method. Also the permit bowldary does not have the necessary staking. When the staking of the highwalls takes place the permit boundary will also be staked. The last issue involves a fuel tank without secondary containment. United realizes the seriousness of uncontained fuel tanks and will promptly remedy the situation. The current contaminated soils will be removed and properly processed. T11e following information should be viewed as a technical revision of the mining plan of the Norwood Pit. "In areas mined at a slope greater than 3H:1 V, the following procedure will be used to ensure that in the event of failure, the failure envelope will stay within the permit area. All slopes will be kept to a maximum slope of 3H:1 V along the permit boundlry. The crest of this slope will be kept 10 feet from the permit boundary. United Companies mines using a O.SH:1 V to near vertical slope. Highwall mining will progress to a 75 foot offset of the crest line. This offset mazks the mid-slope of the final 3H:1 V slope. Both boundaries will be staked prior to mining in the area. This offset serves two purposes. First, the volume of material left in the highwall will allow the crest to be pushed towards the toe with the final slope of 3H:1 V requiring no backfill material. Secondly, this offset provides additional slope safety. It should be noted that the current highwalls with O.SH:1 V slopes demonstrate a greater than 1 safety factor. This is demonstrated through no evidence of slope failure during the life of the pit. However, a failure would be governed by the internal angle of friction of the material. This would limit the failed slope to an angle of 38 degrees or ~1.3H:1 V. This failure would not only stay within the permit azea, it would stay within the final slope envelope." Pboae: (303) 3465] 96 Fax (303)-346.6934 E-Mail: lewicki7~attbi.com The above procedure of staking both the final crest and the mid-slope of the pit walls will become standard practice for United Companies. Through the use of proper staking the risk of slope failure encroaching into adjacent property will be remove;d.