HYDRO27475 - Laserfiche WebLink

Home Browse Search

iii iiiiiiiiiiiu iii ~ STATE OF COLORADO Roy Romer, Gove DEPARTMENT OF NATURAL RESOURCES MINED LAND RECLAMATION DIVISION FRED R. BANTA, Dlreetor April 7, 1989 Mr. Ridc Mills Colorado Yampa Coal Company 29587 Routt County Road No. 27 Oak Creek, CO 80027 Re: Channel Certifications - Drainages 7, 31-1, 31-2, 41, 51, 51W Eckman Park - C-81-071 Dear Mr. Mills: We have reviewed the ACZ and Ground Engineering Consultants (GEC) inspection reports for the above-referenced channels. The ACZ reports indicate unresolved problems and incomplete construction as of September 30, 1988 for Channels 31-1, 31-2, 51 and 51 W. It is possible that all of the remaining problems were specifically addressed during the October 31, 1988 inspection, which is referenced in the November 1, 1968 letter from Conrad Parrish. The final inspection report, however, has not been submitted. Please review the inspection reports, then submit additional certification inspection reports which clearly indicate that all unresolved problems were checked and corrected. Perhaps the October 31, 1988 inspection report will provide all of the remaining required information. We note that the GEC reports indicate that in some areas, riprap gradations are close to the required specifications, but absolute compliance is not indicated. Specifically, as-built gradations are not included for Area 31, and the gradations for Areas 41 and 51 indicate that the as-built gradation includes materials that are significantly smaller than the design specifi- cations. Refer to Tables 1 and 2 for the actual numbers. Please provide statements that are certified by a registered professional engineer which clearly indicate that the as-built riprap gradations for Areas 31, 41 and 51 are adequate to satisfy the design specifications for these channels. Finally, the GEC reports indicate that rounded to subrounded rock was used in the channels. Most riprap specification require the use of rock that is not rounded, and if rounded rock is used, gradation size is usually increased. We understand that the permit approval did not specifically require more angular rock. Future projects should be designed to use more angular rock, or a size adjustment should be included if rounded rock is used. 215 Centennial Building, 1313 Sherman Street Denver, Colorado 80203-2273 Tel. (303) 866-3567