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repair. However,- . it would seem that the flume could continue to <br /> give service for. .an. extended period. if the. undermining condition <br /> could be stopped. <br /> Correction of the problem by this method would require the <br /> following steps: <br /> 1. Excavation : of both sidewalls` and headwall as required to <br /> view and repair the washouts. <br /> 2. Repair of. - the washouts through the, placement of select <br /> granular material fully compacted to level of new subsoil <br /> drainage system. <br /> 3. Repair of inaccessible washouts under the flume through hand <br /> placement of concrete fill, pressure grouting, and/or. hand <br /> placement and compaction of granular material . <br /> 4. Placement of a 12" perforated drain pipe parallel to . each <br /> sidewall and to the slope of flume floor. The . drain pipes <br /> would be placed in a 3 ' x 3 ' gravel pack with filter fabric. <br /> 5.. Placement of four risers south of the headwall for flushing..- <br /> and observing operation of dewatering system. <br /> 6. Hackfill and compaction of all excavations with select <br /> granular material. <br /> 7. Placement of ..an approximately 10 foot wide strip of one foot <br /> thick grouted riprap at each sidewall from. top. to bottom. <br /> 8. Restoration of site. <br /> If it was decided to replace the existing flume with a new, . <br /> heavier structure, added costs -. for removal of the old concrete • <br /> and placement of.- the new flume could be expected. . The subsurface <br />