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<br />i <br /> <br />~9- <br /> <br />Membrane methods -- The blanketing methods of sealing have been <br />used to a limited extent in controlling seepage from short sections of canal <br />above troublesome seepage areas, but the major use of the methods has <br />been in ponds. The common procedure has consisted of: (1) spreading <br />from 1/4 to 3-inches of clay (1 to 25 lbs/sq.ft.) over the leaky area, and <br />(2) harrowing the clay into the sub-soil and then compacting the mixture. <br />The main problems have been: (1) insufficient clay used and (2) erosion <br />at water line in pond. <br /> <br />. <br /> <br />Clay Testing <br />Since the clay sampling as represented in TABLE II is..!!2! of a <br />comprehensive nature, interpretations at this time in regard to the quality <br />of the various clays could be misleading. Comprehensive sampling of <br />deposits that have been developed already is planned for this coming summer. <br />However, even though detailed interpretations cannot be made at this time. <br />" " <br />the testing represented by TABLE'II can be discussed in a general way. <br />Particle ~-- The particle size testing of grit (sand) content <br />and colloidal yield (silt-free clay) gives a general idea of the particle size <br />range in the clay sample. Contrary to popular belief. a high colloidal yield <br />alone does not insure good sealing results. For example, in sealing coarse <br />rocky soils a bigll colloidal yield clay alone, such as a Wyoming high-swell <br />bentonite in most cases will not hold. In rocky materials, the grit content <br />is also important because of its ability to bridge over and plug large voids <br />or holes. On the other hand, for sealing sandy soils it is not good economy <br />to haul. for example, 4 tons of sand for every 6 tons of clay. In other words, <br />the sand in this latter case is sheer waste whereas in the case of rocky soils <br />it is most essenti.al. <br /> <br />1035 <br />