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<br /> <br />STATE Or COLORADO Hn:rlnHn O~IM ~•~w ~~~~~~~ <br />DEPARTMENT OF NATURAL RESOURCES <br />D. Monte Pascoe, Executive DHector <br />iiiiiiiiiiiuiuiii <br />999 <br />1VIINED LANs RECLAMATION <br />423 Centennial Building, 1373 Sherman Street <br />Denver, Colorado 80203 Tel. (303) 839-3567 <br />~~ <br />David C. Shelton <br />December 11, 1980 DITeClO~ <br />T0: Jim Herron <br />FROM: Jim Pendleton ~- <br />RE; Dorchester-Fr to R~Fi1I and Processing Waste Disposal Bank <br />Stability Analyses-~ <br />I have reviewed the materials submitted by Dorchester-Fruita in support <br />of the technical revision application for a processing coal waste bank. <br />Z forward the following comments for your consideration. <br />Rock Fill at the Fruita bl Mine <br />1. The rock fill design conforms with the valley fill regulations of <br />our permanent regulatory program with the exception of subdrain require- <br />ments. Because of the rock fill's granular nature the subdrain requirements <br />may be unnecessary. <br />2. The stability analysis determined a minimum static safety factor of <br />1.65, and a pseudo-dynamic (not required by regulation) safety factor of <br />I.93. - <br />3. The input parameters of the analysis are well justified with one <br />possible exception. The analysis assumes a phreatic surface deep within <br />the rock fill. No justification for this assumption is presented in the <br />report. I recommend that the consultant, GTL Geotesting Laboratories, Znc „ <br />be requested to present a justification of their assumption. Z further <br />recommend that a groundwater observation piezometer be installed at the <br />toe of the fill and monitored on a quarterly basis to verify the degree <br />of subgrade saturation, <br />Coal Processing Waste Bank <br />1. The coal processing waste pile design conforms with the regulatory <br />requirements, including the installation of a durable rock drain ( a <br />minimum 9 feet high by 10 feet wide) for the entire 900 foot length of <br />the proposed fill. <br />~~. <br />(cont'd) <br />