In 1992-98 15.000-20.000 utility poles in Denmark received remedial treatment against decay with fused Boron-rods (IMPEL®). Economically simple, the Impel-rods are placed with the PillarTreat Method as concentrated depots in the ground-line. From there it is distributed by diffusion through the natural moisture in the wood, which ensures that it reaches moist wood in that parts of the pole where decay hazard is greatest. Thus, the amount of Boron that is considered not to cause environmental problems can be limited to what is essentially necessary. 832 of these poles were re-inspected between 1996 and 2000. The time until complete dissolving occurred was measured. Boron distribution and moisture content were analysed. From this data survival probabilities were calculated and a maintenance program established. Even 8 years after remedial treatment Boron concentrations at about the threshold of 1 kg boric acid/m3 could be found in poles that were standing in wet clayey soil. Most interesting, the Impels were completely dissolved 4 years before. Thus, Impel-rods can be inserted periodically with intervals of about 5-8 years depending on the local conditions. When replacements are combined with condition monitoring the replacement intervals can be statistically adjusted for individual lines.

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