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,~ <br />_f' UII'AIIIMI'NI (11 NAlllll Al. IIlSnI~ III IIIIIIIII IIII III `~ <br />• 11. Mnnic I'a mu~• Cu:cul rvr Uu rctur <br />999 <br />A1lNlr.U L~1N1) I{I'.(.LA~IA't'ION <br />~Q <br />423 Centennial Budding, 1313 Sherman Street <br />-. _ -•_ .- Denver, Colorado 80203 Tel. (303) 839-3567 <br />~~t°" David C. Shelton <br />December 11, 1980 Director <br />2b: Jim Rerron (/„ 1~ <br />FROM: Jim Pendleton <br />;,-r`^~ <br />RE: Dorchester-Fr~~ta Ro~ Fill and Processing faaste Disposal Bank <br />Stability An~Iyses ~ ',. <br />I have reviewed the materials submitted by Dorchester-Fruita in support <br />of the technical revision application fora processing coal waste bank. <br />I forward the following comments for your consideration. <br />Rock Fill at the Fruita #1 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. She stability analysis determined a minimum static safety factor of <br />1.65, and a pseudo-dynamic (not required by regulation) safety factor of <br />1.93. <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, CTL Ceotesting Laboratories, Inc., <br />be requested to present a justification of their assumption, 7 Further <br />recorrmlend that a groundwater observation piezometer be installed at the <br />toe of the Fi11 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 4 feet high by 10 feet wide) for the entire 900 foot lenyth of <br />the proposed fill. <br />(cont'd) <br />