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Mountain Coal Company West Ellt Mine F.xltibit 51 Lower Refuse Pile area has a maximum storage capacity of approximately 49,000 cubic yards. Visual monitoring of the topsoil pile will be performed on a monthly basis to assure that any possible slumping will be tspaired as soon as possible. 4.0 SUBSOIL STORAGE The subsoil stockpile lies immediately south of the maximum southom extent of the pile and west of Sylvester Gulch. The height of the pile varies with the volume in storage and will vary with each phase. The maximum amount of material which will be stored is estimated to be approximately 45,000 cubic yards. Acrow-section of the pile has been pnpared showing the plle at !ts anticipated maximum height (see figure LWP-0OS in Appendix D). Visual monitoring of the subsoil pile will be performed on a monthly basis (and reported is quarterly inspections) to assure that any possible slumping will be repaired as soon as possible. S.0 GEOTECHNICAL ST17D1ES S.1 )H1eld Fnveatlgatloa A subsurface field investigation was conducecd on the lower refuse pile site. This :investigation otntststed of performing nine soil borings, installing of five piemmeters, excavating two tat pits, and performing four in-situ permeability tests. This work was conducted in May and June of 1985. The :oil boring work consisted of completing. nine soil borings with the use of a drilling rig operated by P&P Drilling under the direct supervision of Rocky Mountain Geotechnical. The soil borings were advaacod using tither a 4-inch flight auger or a 6-inch hollow amm auger depending on drill hole conditions. Standard Penetration Tests were performed at designated intervals using the appropriate ASTM procedure. Bag samples were talarn of all soli samples. At several locations, Shelby tubes were pushed into the underlying stratum soils to obtain samples suitable for :hear testing. The logs of the trine soil boring holes are found in Appendix E. The locations of the holes are shown on Figures LWP- OOZ to LWP-004. Two tests pits were excavated with a small backhoe supplied by Mountain Coal Company and logged by Rocky Mountain Geotechnical. The test piu were created to obtain information on debris flow. Through the use of the two test pits, six of the various debris flow events, as described in the geology part of this report, were determined. These holes were later bacld'illed to the original ground surface. 8