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<br />Monument Lake Dam Feasibility Study <br /> <br />27 <br /> <br />.- <br />BOYLer <br /> <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />Chapter IV - Formulation of Altemalives <br /> <br />collect all seepage through the embankment and foundation soil. The embankment will then be <br /> <br /> <br />re-constructed with compacted fill to its current geometric configuration. <br /> <br />Embankment Alternative E2 - Blanket Drain System <br /> <br />As shown in Figure IV-7, this alternative has less drain materials than Alternative EI, but <br /> <br /> <br />more excavation and embankment fill. The top portion of the embankment is excavated to <br /> <br />elevation 6920.0, and the embankment downstream of the centerline will be excavated to the top <br /> <br />offoundation soil. All of the existing trees and shrubs on the embankment will be cleared and aI: <br /> <br /> <br />the roots will be grubbed. A 50-foot-wide horizontal blanket drain, consisted of2 feet of drain <br /> <br /> <br />gravel sandwiched between two I-foot-thick filter/drain sand layers, will be constructed at the <br /> <br /> <br />bottom of the embankment. An 6-inch pve slotted toe drainpipe is embedded in the drain gravel <br /> <br /> <br />layer. The internal drains will filter and collect the seepage through the embankment and <br /> <br />foundation soil. The embankment will then be re-constructed with compacted fill to its current <br /> <br /> <br />geometric configuration. <br /> <br />For both alternatives the upstream slope above elevation 6920.0 will be protected with 2 <br />feet of rip rap over I-foot of bedding material. The dam crest will be protected with I-foot of <br />compacted aggregate base course. The downstream slope will be protected with seeded topsoil. <br />An 85-foot-long concrete retaining wall will be required on the left abutment for the new fill. <br />The existing 36-inch old spillway on the right abutment will be excavated and backfilled with <br />compacted fill. <br /> <br />Instrumentation for the dam would include eight embankment settlement points on the <br />dam crest, and six piezometers on the dam crest and toe of the dam. <br /> <br />C. Outlet Works Alternatives <br /> <br />Three alternatives were developed to re-Construct the outlet works for Monument Lake <br />Dam. The alternatives will require the excavation and removal of the existing outlet works. The <br />new outlet works will be constructed along the existing outlet works alignment. The alternatives <br />have an impact type basin on the downstream end of the outlet works, which then flows into the <br />downstream stream. <br />