of flowing water and are probably not practical in conveyance channels. The cationic asphalt emulsions have remarkable properties for bonding lissimilar materials and are now being tested in conjunction with einforcing fabrics. Cost. The cost of cationic emulsions containing 5.5 pounds of ashalt per gallon should be about 25 cents per gallon. SS-13 SS-13 is a commercially available emulsified compound designed to be added to ponded water, where it is carried into the soil with the seeping water. The material contains resinous polymers that react in the soil to form a lattice of long chain molecules, which restricts water movement. Laboratory tests have been conducted in soil columns to show that. the SS-13 material penetrates sandy loam soils at least 4 inches below the soil surface and thus greatly reduces permeability of water in this treated soil zone. Laboratory and field tests have shown that the material will reduce seepage by over 70 percent under favorable soil conditions. Field tests conducted by the Bureau of Reclamation at the Salt River project in Arizona and by the manufacturers of SS-13 have shown that the material remains effective for more than 3 years if it is not subjected to drying. The toxicity of this material other than that associated with the use of diesel oil as a part of the emulsion complex does not appear to be a problem. The material has been fed to cattle and has been consumed by humans with no ill effects. Field tests have shown that the effectiveness of the material is essentially destroyed by alternate periods of wetting and drying. This problem has not been well defined and is currently under investigation. SS-13 Cost. The cost of material is dependent upon the ratio of volume to wetted perimeter in the channel or reservoir to be treated. costs $1 per million in the gallon and is applied at a rate of about 1,000 parts Effectiveness ponded water. WATER REPELLANTS Many chemical compounds will effectively make soil water repellant. These include silicons, various combinations of salts and soaps, and other materials such as quaternary ammonium salts. The reaction of these materials can be simply explained by saying that the molecule has a head which is attracted to the soil particle and a tail that is repellant to water. A number of compounds have been tested at the U.S. Water Conservation Laboratory, Tempe, Ariz. It has been found that the problem of making soils water repellant is not difficult. Effectiveness of a given chemical does vary with soil type, however, and it is necessary to conduct testing on each soil to determine the best material and the optimum rate of application for use. A small field plot sprayed with a water repellant, with no other treatment, has consistently produced from 40 to 60 percent runoff of rainfall The water repellants can be sprayed on the surface of soil that has been previously treated with an asphalt emulsion to stabilize the soil against erosion. Large field plots treated with both the asphalt emulsion and the water repellant have produced runoff ranging from 86694 0-62-6 80 percent to over 90 percent, depending upon quantity and intensity of rainfall. Toxicity Toxicity is not expected to be a problem with the use of the water repellants, but it must be considered and is currently under investigation. Some of the water repellant chemicals do deteriorate under continued high temperature, whereas others do not. Selection of water repellant will therefore depend upon climatic as well as soil conditions. Cost The cost of water repellants tested to date varies from about 45 cents to $1 per pound. The rate of application required to waterproof the soil has ranged from 20 to 500 pounds per acre. The rate of application depends primarily upon the soil, as it takes less for sands. than for clays. Water repellants are already competitive on the market, and it is doubtful that costs will be greatly reduced by increased demand. Soil dispersants Studies of leaking ponds in the Ozark region of Missouri indicate that chemical soil dispersants, such as some polyphosphates, will reduce seepage in ponds constructed in coarsely aggregated clay soils. Chelating resins may be even more effective in forming polyvalent cation complexes, thus dispersing the clay colloids through destruction of the aggregate bonds. Provision must be made for bed strength beneath the dispersed layer to prevent "blowout" failures. Studies with soils from leaking ponds in Missouri indicate that mechanical dispersion, such as by the trampling of animals, is very effective in reducing seepage. Machinery to tread and disperse the soil beneath the water in ponds so as to produce a compact subsurface layer beneath a dispersed seal may be about as satisfactory from the standpoint of effectiveness and more economical than chemical treatments or sheet membrane liners. Research LININGS Considerable research on the development of lining for controlling seepage has been conducted at Logan, Utah. This work has includedEarth material of several types-used both as blankets and as waterborne sediments. Earth stabilized with chemicals applied to the subgrade as sprays and mixed with the subgrade material or as specially imported earth material to form a stabilized and waterproof lining. Earth stabilized with portland cement; that is, soil cement. Prefabricated asphalt liners, for use both as buried and exposed membranes. Asphaltic concrete. Prefabricated liners consisting of plastic-coated paper and paper cloth, resin impregnated paper, and similar materials. Portland cement concrete and shotcrete. Plastic films, such as polyethylene, vinyls, mylar buried and exposed. Rubber, such as butyl, neoprene, polyisobutylene. Many of these materials cannot be classified as new, but the methods developed for their use frequently were new or the material was modified for better adaptation to the use under consideration. Any of the linings or treatments, except for cleaning or enlargement, tend to reduce seepage. Working or compacting the subgrade will reduce seepage to a degree, depending on the operation. If the subgrade material is gravel, a topping of sand will reduce seepage. Complete watertightness is seldom achieved. Of all the lining material mentioned, butyl sheeting (fig. 8), plastic film, and prefabricated liners (fig. 9) are the most watertight, and even these cannot be depended upon to be fully watertight, owing to the possibility of damage during installation and faulty joints. Site conditions and other factors, including canal and reservoir management practices and cost, determine the type of lining that should be used. Materials such as butyl and plastic, in particular, appear to have great potential as liners. Benefits and limitations of lining Results to date indicate linings may be classified into four groups with the following benefits and limitations: (1) Paved or hard-surfaced linings: Materials: Concrete, brick. Benefits and limitations: Prevents seepage, scour, and controls weeds; requires little maintenance; permits wider range of velocities; resists damage from livestock and equipment. (2) Exposed membrane linings: Materials: Exposed asphalt lining. Benefits and limitations: Prevents seepage and controls weeds to a degree; treatment with fungicide chemicals necessary; must be cleaned with care; not suitable where subject to heavy animal traffic. (3) Conditioned earth linings: Materials: Natural earth compacted; earth stabilized with chemicals, with small amounts of asphalt, or with small amounts of portland cement. Benefits and limitations: Controls seepage but weed problem is same as in unlined canal; frequently subject to scour unless protected with nonerosive topping such as gravel; cheap to construct under ideal conditions; velocities of water flow limited to 3 ft./sec.; protective cover desirable. (4) Buried membrane linings: Materials: Asphalt and plastic membranes. Benefits and limitations: Controls seepage but frequently adds to weed problem and the care must be used in cleaning; velocities of water flow limited to 3 ft./sec. Virginia tests Although most studies to control seepage have been conducted in the West, three plastic pond liners have been installed in Virginia. The dark-colored vinyl film used in these tests was manufactured with a plasticizer not affected by fungus. |