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CONSTRUCTION CONSIDERATIONS   R A.` ` Construction Timing(#` XX` ` The Lower Mundo Lake Dam area does not have a true year round construction season. However, the schedule should be implemented such that construction can be ongoing throughout the year. The length of construction for the concept design alternatives is highly dependent on the choice of foundation improvement mentioned above, with removal and replacement requiring the most time. It is noted that the embankment can be raised concurrently with an upstream toe cutoff option and partially with the removal and replacement option and the cutoff wall through the dam option. The spillway remediation can be performed concurrent with all options. Prior to constructing the embankment raisure, the outlet pipe must be extended.(#`  R XX` ` 1.X Embankment Raisure(# XX` ` X Prior to placing the extended rockfill toe, sand blanket, etc., the downstream slope must be stripped of vegetation and organic material. An impervious zone must be extended to new top of dam. The new downstream slope must be seeded to provide erosion control. The existing piezometers must be extended or replaced to accommodate the new dam height. Final design will specify lift thickness, compaction effort and moisture control. The sand blanket must be placed and compacted in such a way that no contamination will occur with the adjacent random fill.(# ,&, ( (Ԍ R XX` ` 2.X Foundation Seepage Remediation(# XX` ` X Both the removal and replacement of the cutoff trench and the addition of an upstream cutoff wall for foundation seepage remediation require that the lake be lowered. The cutoff wall through the dam option will require lowering of the lake but not complete drainage. Therefore, use of the reservoir will not be available during construction for the first two options listed above. The upstream toe cutoff would result in a shallower cutoff to be excavated either in panels with a clam shell excavator or as a continuous trench with a backhoe. (#  R\ XB.X` ` Reservoir Operation During Construction(#` XX` ` Options requiring the lake to be drained will require a cofferdam upstream of the existing embankment to allow for diversion of low flow and small floods around the right end of the embankment. This will most likely be accomplished by extending the outlet pipe through the cofferdam and using the outlet for diversion. A further evaluation of diversion capacity will be made during final design. (#` XX` ` If a centerline cutoff trench is used, a cofferdam would not be required. Top of dam during construction would be elevation 7326 or about one foot below spillway crest. However, the reservoir should be lowered below normal level.(#`  Rr# XC.X` ` Foundation Excavation and Remediation(#` XX` ` The two foundation treatments investigated for conceptual design are: (1),&, ( ( remove and replace the existing right side embankment and cutoff trench or (2) install an upstream toe cutoff wall which would result in a shallower trench to be excavated either in panels with a clamshell or as a continuous trench with a backhoe. Therefore, a stockpile area which will probably be located downstream of the existing embankment to temporarily place excavated embankment and foundation material. With careful sequencing, some of the excavated material can be utilized in the random fill section of the new downstream shell. If necessary, some can be placed in an upstream loading berm to improve seismic stability. (#` XX` ` The equipment yard and construction office will also most likely be located downstream of the existing embankment. (#` XX` ` For option (1) listed above, some dewatering of the lower portion of the excavated area will be necessary. The number of stages of well points will depend on the depth of excavation that is selected or deep wells may be feasible. Since the lake can be drained to about elevation 7290 only that part of the excavation below elevation 7290 would require dewatering. The downstream foundation for the embankment raisure from the outlet to the right abutment is generally soft and marshy. Some dewatering and deep stripping may be required to establish a satisfactory foundation.(#`  R XD.X` ` Embankment Materials(#` XX` ` The existing embankment will remain in place for all of the conceptual design alternatives. However, the right side of the embankment would be excavated for the remove and replace foundation improvement option. The excavated embankment material would be stored and replaced into the embankment.(#` ,&, ( (ԌXX` ` For each of the concept design alternatives the embankment will be raised some amount. If the embankment is raised to elevation 7338, an auxiliary spillway will not be needed and the material must be obtained from a borrow area. If the embankment is raised to elevation 7336 and an auxiliary spillway is constructed then part or all of the material can come from the spillway excavation. The majority of the material required to raise the embankment can be random fill. However, part of the embankment raisure at the top must be select material to control seepage. This select material must have at least 25 percent passing the No. 200 seive that will classify as a clay (CL). The random fill can be any suitable material. The embankment fill materials should be compacted to not less than 95 percent standard density.(#` XX` ` As stated earlier, the rock fill toe will either be obtained from a local quarry source or an off reservation source. The sand drain will be composed of concrete sand and will be brought in from off the reservation.(#` XX` ` Where riprap is required to prevent erosion of the floor and side slopes of the spillway, it will be sized to withstand the spillway flow velocities if it is chosen for final design. Otherwise, standard New Mexico Highway Department wire enclosed rock will be chosen for final design.(#` XE. Additional Exploration(# XX` ` Two additional borings are planned on the dam axis near the right abutment to provide needed information on the top of rock and quality of rock for tying the seepage cutoff wall into the abutment. Exploration is also needed near the lake to determine a borrow source for impervious and random fill.