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<br />\/ - Climax Molybdenum Company <br />September 22, 7987 . <br />Page 5 <br />L~dward•Clyde Cortsultartts <br />when the soil surface is rough. Soil particles about 0.7 mm in diameter are <br />generally more erodible than those of larger or smaller particles. <br />Dust treatment with palliatives has generally been developed for roads <br />with the use of binder soil, such as-clay, chlorides, or other additives <br />applied by maintenance forces._ Dust palliatives were developed to serve <br />two purposes: (t) elimination of dust, and (2) the preservation of the <br />soil-aggregate surface. For roads, a comparison is generally made between <br />the cost of adding surface binders and the application of a dust palliative. <br />Sodium chloride is sometimes used as a dust suppressant. It can help <br />retard evaporation, but it will not absorb moisture from the air. When <br />rock salt is used, it is usually mixed in the upper 2 inches of material <br />at the rate of 2 1/2 to 3 pounds per square yard. water is also added to <br />the mixing process. <br />Calcium chloride has been used because of its "hygroscopic" nature, (it <br />attracts moisture), and because it is "deliquescent", (it dissolves itself <br />in the moisture which it attracts). Calcium chloride scattered over a road <br />// has been reported to absorb and hold from 2 to S times its weight in water. <br />The chemical thus serves to keep the surface damp and dustless for con- <br />. siderable periods of time. In dry weather, calcium chloride will absorb <br />moisture from Lhe air during periods of high humidity, such as at night. <br />Calcium chloride is susceptible to dilution by rain and gradually leaches <br />into the soil. <br />Calcium chloride is available in flake and granulai form. Best results <br />are obtained when mechanical spreaders are used and when the material is <br />applied after a rain. The initial application in the spring is made at <br />a rate of from 3/4 to 1 7/2 pounds per square yard. Later application <br />requirements during the summer will vary, however, a total of t t/2 to <br />2 t/2 pounds per square yard say be required depending on the texture <br />of the surface, previous amounts of stabilization, dryness of the season, <br />and the amount of traffic. Magnesium chloride has also been used with <br />the method of application being similar to that used for calcium chloride. <br />Wind breaks, shelterbelts, and contour strips can help lessen wind erosion <br />by reducing wind velocities at the surface. A rough surface helps decrease <br />wind velocities and trap some of the moving particles. Picket fences, geo- <br />textiles and burlap screens can also be used as wind breaks and can be <br />moved from place to place. <br />Application of various types of.bituminous surface treatments have been <br />used for dust control on unsurfaced roads, however, we feel these would be <br />extremely costly for tailing applications and would Beverly impede their <br />~~ permeability. <br />