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• Section 1 <br />Removal of Topsoil and Organic Material <br />Topsoil removal operations began in the Section 16 Fill azea on August 24, 1992. <br />Topsoil depths ranged from a few inches near the tops of the south and east facing slopes on the <br />north side of the fill to several feet along the drainage course where the rock underdrain would <br />later be placed. <br />On September 24, 1992 topsoil removal and removal of organic material was complete <br />in the fill area. <br />Photographs 1 through 5 verify removal of topsoil and organic material from the fill area. <br />Together photographs 1 through 5 form a panorama of the fill area. Photograph 1 is looking <br />south, and the panorama proceeds to looking northwest in photograph 5. <br />Once topsoil was removed it was apparent that the bottom of the drainage was filled with <br />a veneer of unconsolidated colluvial material. The colluvium was likely transported from <br />weathered outcrops along the side slopes of the fill area and deposited in the bottom of the <br />drainage. The veneer ranged in thickness from 12 feet at the toe location to less than 3 feet <br />thick at a point approximately 350 feet up the drainage from the toe. Photographs 6 through 9 <br />show this area prior to excavating the veneer. <br />• Although Colowyo was not required to verify bedrock conditions at the revised toe <br />location, it was apparent that [he unconsolidated material should be removed to reach competent <br />bedrock. <br />In addition to exposing the colluvial veneer, the topsoil removal operation also revealed <br />the alignment of the underdrain needed to be shifted westward to correspond to the actual <br />topographic low of the drainage. Prior to topsoil removal the topographic low appeared to be <br />a bifrication of the drainage and was oriented SW-NW. Photograph 10 shows the natural Swale <br />that required the orientation of the underdrain to be changed. <br />Photographs 11, 12, and 13 show the excavation of unconsolidated colluvial deposits to <br />bedrock. Photograph 14 shows completion of the excavation to bedrock. <br />A minor seep (estimated at less than 1 g.p.m.) was encountered while excavating to <br />bedrock. The location of the seep is behind and to the left of the pickup truck shown in <br />photograph 14. <br />Since the controlled underdrain would be in contact with the seep there was no need to <br />design a lateral from the underdrain to accommodate the seep. <br />• <br />Section 1 -page 1 <br />