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• fill be wmpacted to a minimum of 95% of its maximum standard Proctor dry density (ASTM D-698). This liner <br />fill should be placed in hfts not to excxed six (6) inches after compaction. We recommend that fill be placed and <br />compacted at approximately its optimum moisture content (+/-2%) as determined by ASTM D-698. <br />No major dilTiculties are anticipated in the course of excavating into the sudicial soils on the site. It is probable <br />that safety provisions such as sloping or bracing the sides of excavations over 4 feet deep will be necessary. Any <br />such safety provisions shall conform to reasonable industn safet}~ practices and to applicable OSHA regulations. <br />The OSHA Classification for excavation purposes on this site is Soil Class C. <br />During the placement of any structural fill, it is recommended that a sufficient amount of field tests and <br />observation be performed under the direction of the geotechnical engineer The geotechnical engineer should <br />determine the amount of observation time and field densih~ tests required to determine substantial conformance <br />with these recommendations. <br />EMBANKMENT GEOMETRY Basal upon slope stabihtycomputations,themodi6ed <br />cmbartk~ncnl slope on the interior fact of the south embankment will be adequate assuming the soils of the liner <br />• arc mixed and the subgrade soils are prepared as described above for a proposed fill slope of 2 %:: 1 <br />(horizontal:verlical). The safety factor against failure was found to be in excess of 2 for the normal high water <br />Icccl, with a steady state scepagc saturation condition in the re.vorkcd soils, with the reworked suberade soils <br />and the ling intact and working and the existing good to very good drainage conditions of the native soils being <br />maintained. Due to the very permeable subgrade soils beneath this site and the lack of a long term high water <br />table, complete saturation otlhc embankment and subgrade sails is not believed to be possible on this site. <br />The stabilit}' of the south facing slopes of the embankment, adjacent to the Coal Canyon Drainage Channel, was <br />found to be adequate, assuming the pond embankment surface and floor surface are reworked according to the <br />recommendations contained in this report. If significant piping of the subgade soils aze allowed to continue, <br />if continued fluids are added to the pond to maintain the maximum water level, as infiltration and piping <br />continues through the subgrade soils, failure of the embankment ~~~11 occur. This failure will probably take the <br />form of a slope soil failure as the piping accelerates from the pond do~mward then horizontally into the Coal <br />Canyon Channel. The presence of the prepared subgrade soils, the thin soil liner and possibly the geotextile <br />fabric arc critical for stability of the slope banks and proper functioning of the sedimentation pond. <br />• <br />