WWW.MEGGER.COM

Treatment of the Soil: Chemical treatment of soil is a good way toimprove earth electrode resistance when you cannot drive deeper groundrods because of hard underlying rock, for example. It is beyond thescope of this manual to recommend the best treatment chemicals forall situations. You have to consider the possible corrosive effect on theelectrode as well as EPA and local environmental regulations. Magnesiumsulfate, copper sulfate, and ordinary rock salt are suitable noncorrosivematerials. Magnesium sulfate is the least corrosive, but rock salt is cheaperand 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 shouldbe kept away from building foundations. Another popular approach is tobackfill around the electrode with a specialized conductive concrete. Anumber of these products, like bentonite, are available on the market.Chemical treatment is not a permanent way to improve your earthelectrode resistance. The chemicals are gradually washed away by rainfalland natural drainage through the soil. Depending upon the porosity ofthe soil and the amount of rainfall, the period for replacement varies. Itmay be several years before another treatment is required.Fig. 19: Trench method of soil treatment 10Chemical treatment also has the advantage of reducing the seasonablevariation on resistance that results from periodical wetting and drying outof the soil. (See curves of Fig. 20.) However, you should only consider thismethod when deep or multiple electrodes are not practical.See Appendix I which describes the use of a nomograph relating length ofrod, diameter of rod, and earth resistivity to earth resistance.Fig. 20: Chemical treatment of soil lessens seasonal variation of electrodes’earth resistance 1110, 11 Source: Reference 20 (page 77)40 1-866-254-0962 www.megger.com Getting Down to Earth 41