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n <br />U <br />-zs- <br />safety was 2.91. Based on the results of the stability analysis, <br />we believe the configuration II-B is inherently more stable than <br />configuration II-A. If at all possible, we recommend construction <br />of the spoil disposal using the configuration identified as II-B <br />RECOMMENDATIONS <br />1. In our opinion, the selected areas can be safely developed as <br />permanent spoil disposal sites. Based on our interpretation <br />of the Federal regulations, we believe that both sites should <br />be designed to meet the requirements of the 816.72 disposal <br />of spoil 'valley fill'. <br />2. It will be necessary to remove all existing vegetative and <br />organic materials from the surface of the disposal sites. <br />Additionally, we believe about 2 feet of the near-surface <br />soils should be stripped from the entire disposal area and <br />saved for re-vegetation of the spoil disposal site surface. <br />• 3. Our stability analysis indicates that foundation control <br />could occur because of the relatively thin, soft foundation <br />layer that occurs at both disposal sites. For this reason, <br />we believe a toe buttress fill is desirable at both locations. <br />The buttress fill should be constructed by excavating a trench <br />about 200 feet wide from the ground surface down to competent <br />bedrock. We anticipate the depth of this trench will range <br />from s feet to a maximum of 20 feet. Soft materials removed <br />by this construction should be stockpiled and used on the <br />surface of the disposal fill to support re-vegetation. The <br />buttress fill should be constructed of sandstone spoil where- <br />ever possible. The buttress fill must be constructed under <br />controlled, compaction conditions because the stability of <br />the overall fill is a function of stability of the buttress. <br />We anticipate the buttress fill to be compacted in layer <br />approximately 2 feet in thickness and compacted to a minimum <br />density of approximately 90 percent of ASTM D lss7 (AASHTO <br />T-180). Placement and compaction of the buttress fill should <br />be observed by our office during the construction procedure. <br />• <br />4. Prior to construction of the disposal fill, we recommend that <br />underdrains be located in all existing natural drainages and <br />at the locations delineated on Figs. 2 and 9. The drains should <br />constructed of durable sandstone rock and should be a minimum <br /> <br />