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' <br />, <br />dam and cover the liner. Place 6-inches of riprap bedding and 12-inches of riprap on the upstream <br />face of the main dam for erosion protecaon. <br />6. Install approximately 500 feet of 4-inch diameter toe drain piping at the downstream toe of the dam. <br />Place the drain inveri approximately 5-feet below grade with a gravei envelop around the pipe. <br />7. Apply 4-inches of gravel to the dam crest for erosion protection in accordance with SEO manual. <br />8. Raise the south dike embankment approximately 2-feet and add riprap to the upstream face for erosion <br />protection. <br />9. Seed all areas above the high waterline disturbed during construction. <br />' Alternative #3 <br />' <br />, <br />' <br />' <br />' <br />' <br />l! <br />' <br />' <br />' <br />, <br />, <br />' <br />This alternative consists of abandoning Gtay No. 3 and increasing the capacity of South Gray Lake by 111 <br />acre-feet. The dam is constructed of low densiry silry sands and would be expected to leak without some <br />measures to control the seepage. The embankment materials encountered in our geotechnical investigation <br />were not as clean or as coarse as at Gray No. 3 and thus not as permeable. An upstream PVC liner was <br />not considered for this dam, but the installation of toe draic�s and seepage blankets was included to control <br />the seepage exiting the dam face. The main dam would have to be raised approximately 3-feet to provide <br />for the additional storage capacity and provide for proper freeboard. The upstream face of the main dam <br />and the two dikes on each end of the main dam will require more riprap be placed to supplement the <br />existing riprap and provide for sufficient erosion protection. <br />The dike on the south side between South Gray and Gray No. 3 will have to be raised approximately 3-feet <br />to provide for the additional storage and freeboard. The dike between North Gray and South Gray has <br />sufficient height and will not have to be raised. <br />Work to be conducted <br />1. Raise main dam and south dike approximately 3-feet. The fill on the main dam to increase the height <br />will be added to the downstream face which will also increase [he stability. The slopes will be <br />constructed to a 2.5 horizontal to i vertical slope. <br />2. Extend the outle[ pipe and construct a headwall and energy dissipater at the downstream end of the <br />outlet pipe. <br />3. Construct a 100-foot wide, 5-foot deep concrete spillway wall with 12-inches of riprap and 6-inches <br />of bedding on the upstream and downstream sides to control erosion. <br />4. Install approximately 3500 feet of 4-inch diameter toe drain piping at the downstream toe and at the <br />dam mid height with a gravel seepage blanket on the main dam. <br />5. Add riprap to the upstream face of main dam and the two dikes to provide for proper erosion <br />protection. 12-inches of riprap will be added to the upper 25 feet of the dam face with 6-inches of <br />bedding being applied only on that portion of the dam embankment that is raised. <br />6. Apply 4-inches of gravel to the dam crest for erosion protection in accordance with SEO manual. <br />7. Seed all areas above the high waterline disturbed during construction. <br />COST ESTIMATE <br />The complete breakdown of the cost of the work proposed for each alternative is shown in Tables <br />Gray Lake-Feasibility Study Page 6 <br />� <br />