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<br />( <br /> <br />o <br />IJ') <br />:-- <br />o <br />c.., <br />~~, <br /> <br />( <br /> <br />L <br /> <br />21 <br /> <br />7.2.3.2 <br /> <br />Synthetic Membranes <br /> <br />(j <br /> <br />Synthetic membranes and their installation techniques have <br />improved to the point where they have become an accepted seepage <br />control measure. Studies by the USBR (1970) show that seepage <br />rates for these liners are much lower than compacted clay and <br />practically zero seepage can be achieved. Therefore, if total <br />seepage control is mandated, then synthetic liners may be the <br />only technical solution. <br /> <br />7.2.3.3 Slurry Cutoff Wall <br /> <br />A slurry cutoff wall would be effective (assuming no adverse <br />effects of saline water on the bentonite slurry and wall cake <br />occurred) at controlling lateral seepage. However, since the <br />main component of seepage will be vertical as shown in Table 7-2. <br />A significant amount of seepage will still occur. Therefore, the <br />use of slurry walls do not appear to be practical for this <br />project. <br /> <br />7.2.3.4 Compacted Clay Cutoff Walls <br /> <br />As with slurry walls, these would control only lateral seepage <br />and not vertical seepage and therefore are probably not <br />applicable for this project. <br /> <br />7.3 Dike Construction <br /> <br />( <br /> <br />Typical dike sections are shown on Figure 9. It has been <br />assumed, for preliminary planning purposes that seepage control <br />consisting of either an 18 inch compacted clay liner or a <br />synthetic membrane liner will be required. The dikes have been <br />shown to have a nominal height of 10 feet. However, higher dikes <br />may be necessary in many parts of the site due to the uneven <br />terrain. <br /> <br />Since detailed topographic mapping is not currently available, <br />the significance of constructing dikes of various heights is not <br />quantifiable. For the dikes, a crest width of 15 feet has been <br />selected to allow for passage of vehicular traffic. The slopes <br />of the dikes should be constructed at 3 horizontal to 1 vertical <br />to minimize erosion problems by wave action. Since erosion from <br />wave action is expected to be minimal, it has been assumed that <br />flatter slopes instead of riprap will be used as a deterent and <br />that periodic maintenance be utilized to insure the integrity of <br />the dikes. <br /> <br />Seepage control for interior dikes will consist of either a <br />continuous 18 inch thick compacted clay liner underneath the <br />dike or a synthetic membrane liner over smooth bedding material. <br />The liners should be constructed by first removing the topsoil <br />and vegetation from the surface, leveling the site area and then <br />scarifying and compacting in place the upper 6 to 8 inches of in <br />situ clayey soils. <br /> <br />c <br />