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<br />1 <br /> <br /> <br /> <br />1 <br /> <br />1 <br />1 <br />SCOPE: <br />PHASE II STABILITY ANALYSIS <br />CAMEO REFUSE DISPOSAL AREA No. 1 <br />CAMEO, COLORADO <br />MAY, 1994 <br />The present Phase II stability analysis of Cameo Refuse <br />Disposal Area No. 1 (CRDA No.l) is presented as an addendum to the <br />Phase I stability analysis submitted by Western Engineers, Inc in <br />February of 1994. The Phase II analysis was requested by Western <br />Associated Coal Corporation in response to the inconclusive results <br />of the Phase I analysis. The present investigation and analysis is <br />based on recommendations made in the Phase I analysis and attempts <br />to more clearly define piezometric levels and pore pressure systems <br />within the pile. The present study includes the results of bailing <br />(removal of water) and water level recovery from certain existing <br />piezometer wells; the findings of drill hole logs; the <br />installation, measurement and evaluation of 30 piezometer (PZ) <br />wells, with hydraulically isolated tips, at four drill hole <br />locations; and stability analyses of two sections through the pile, <br />which were identified in the Phase I study. It must be noted at <br />the onset that the extent of the present investigation and <br />subsequent analyses provides a general representation of conditions <br />at specific locations within the refuse pile. <br />' BAILING: <br /> <br /> <br /> <br /> <br />1 <br /> <br />On March 11, 1994 bailing operations were initiated. Bailing <br />was performed with an 1.25-inch diameter by 6-foot long bailing <br />tool (approx. 1-gal capacity) which was lowered and raised from the <br />existing 2-inch diameter piezometer wells with a hydraulic wire <br />line winch attached to a mobile B-50 drill rig. Over a 3-day <br />period 8 of the 19 existing wells were bailed. The 11 wells not <br />bailed were dry to their respective tip depths. Bailing was <br />conducted to verify that the various wells were not sealed and to <br />judge the general permeability of intercepted water bearing zones <br />based on drawdown and recovery rates. In instances where companion <br />wells were nearby, the bailing effort was used to observe draw down <br />effects in such companion wells. Draw down effects in a companion <br />well would indicate water path connections and/or less pervious <br />boundaries between the bailed well and the companion well. <br />Transmissivity rates were calculated from semi-logarithmic Time- <br />Drawdown and Residual-Drawdown (recovery) graphs, presented as <br />Plates 1 through 10 of the Appendix. Transmissivity (T) is the <br />rate at which water is transmitted through a 1-foot width of ar. <br />aquifer under a hydraulic gradient of 1 ft/ft. Transmissivity is <br />measured in gallons per day per foot through a 1 foot square <br />vertical section extending the full saturated height of an aquifer. <br />In order to convert transmissivity results to permeability rates, <br />intercepted aquifers were considered to have a saturated height of <br />10-feet, based on subsequent drill log information. Each of the <br />wells were bailed at a constant rate, then allowed to recover. In <br />