C153445 Feasibility Study - Laserfiche WebLink

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Ab~ndonment was accomplished by plugging the outlet with concrete. A concrete bulkhead ~as placed on the upstream end of the outlet. The reservoir water level was below the outlet. Concrete w?s then pumped into the outlet from the do~nstream end. The concrete work is not included in the study' There is a channel and pond directly below the outlet which must be filled. Seeps are likelY to occur through the embankment and possibly along the plugged outlet so the fill will include a filter blanket in the channel and a portion of the pond. A 6", drain pipe will be incorporated to remove water from the filter. The pipe will allow drainage from the filter without having to extend the filter. The filter will then be covered and the rest of the.pond filled with cammon material. The area will be con- toured to ma~ch the surrounding topography and seeded. 4. Middle south dike filter. There are several methods that can be considered for control- ling seepage below the South Dike. These range from complete seepage cutoff to controlling seepage at the exit point. An upstream blanket of impervious material placed and com- pacted in the reservoir area upstream of the dike would lengthen the seepage path and thereby reduce the exit gradients and the quantity of seepage. This requires large quantities of suitable material, quite possibly a problem in this area. Largequantities of impermeable material would be needed because the blanket would have to,extend several hundred feet into the reservoir to assure a cutoff. The material most readily available is ,shale that severe- ly cracks when dessicated. making it unsuitable. M~terial would have to be hauled in from a distance and carefully placed. and compacted, making this solution very expensive. Any processing to increase sui tabili ty would also' serve to increase costs. A drainaeje berm placed on the downstream portion of'the embankment and foundation would serve to provide stability to those portions by virtue of its added weight. Seepage would still be present, but potentially catastrophic results would be alleviated. The seepage could be collected and monitored at a convenient point. Material for ~ berm will have to meet criteria insuring free drainage while not allowing piping of foundation or embankment material. . A filter: blanket and berm is the recommended solution" increasing the stability and con~rolling the seepage. This method will probably be less expensive ~nd will assure stability, where a cut off blanket may develop cracks and is more expensive. There are two main design considerations involved with the filter blanket and berm. First, the filter blanket must be of suitable material to allow seepaeje but not allow piping to occur. The second consideration is to hove sufficient weight of material on top of the filter blanket to ossure that the embankment and foundation will not f~il. These design considerations are thoroughly discussed in the following paragraphs. -27-C.