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A measurement of a soil’s ability to conduct electrical currents.
Corrosion of unprotected steel underground tanks is caused by stray electrical currents coursing through the surrounding soil. Current flowing away from a tank carries with it tiny bits of metal. Over a period of time, in an area where there is a high level of electrical activity, this results in deterioration of the tank walls.
But some soils are not conducive to electrical activity. Very dry, sandy soils, for instance, are less likely to cause corrosion than are soils composed principally of moist clay.
Corrosion experts have developed a method for determining the likelihood of tank corrosion at a particular site by measurement of the resistivity of the soil at the location.
Federal tank regulations require protective measures for steel underground tank systems. The regulations, however, exempt a steel tank installed at a site “determined by a corrosion expert not to be corrosive enough to cause it to have a release due to corrosion during its operating lifetime.” The federal rules also require that the owner or operator of an exempted tank maintain certain records on the tank for its remaining lifetime.