40 www.megger.comTreatment of the Soil: Chemical treatment of soil is a good way to improve earth electrode resistance when you cannot drive deeper ground rods because of hard underlying rock, for example. It is beyond the scope of this manual to recommend the best treatment chemicals for all situations. You have to consider the possible corrosive effect on the electrode as well as EPA and local environmental regulations. Magnesium sulfate, copper sulfate, and ordinary rock salt are suitable noncorrosive materials. Magnesium sulfate is the least corrosive, but rock salt is cheaper and does the job if applied in a trench dug around the electrode (see Fig. 19). It should be noted that soluble sulphates attack concrete, and should be kept away from building foundations. Another popular approach is to backfill around the electrode with a specialized conductive concrete. A number of these products, like bentonite, are available on the market. Chemical treatment is not a permanent way to improve your earth electrode resistance. The chemicals are gradually washed away by rainfall and natural drainage through the soil. Depending upon the porosity of the soil and the amount of rainfall, the period for replacement varies. It may be several years before another treatment is required.Chemical treatment also has the advantage of reducing the seasonable variation on resistance that results from periodical wetting and drying out of the soil. (See curves of Fig. 20.) However, you should only consider this method when deep or multiple electrodes are not practical.See Appendix I which describes the use of a nomograph relating length of rod, diameter of rod, and earth resistivity to earth resistance.
