I hope this helps,
My layman's answer (inso far as I'm not a scientist, but educated as an experienced Realtor), would be to agree with Eric that it depends on the buyer. However, as a general rule if you are concerned at first glance, then chances are other future buyers may be too! If there are other great choices in terms of housing that you like, I'd look there first before buying a home near the power lines. Given two identical homes, one being near power lines, and the other not, I'd pick the one that doesn't sizzle in the rain...
Best of luck!
Ashley, J.R.; Beatie, R.E.; Heneage, J.F.
Electro 98. Professional Program Proceedings
Volume , Issue , 9-11 Jun 1998 Page(s):171 - 179
Digital Object Identifier 10.1109/ELECTR.1998.682111
Summary:A 1979 epidemiologic study in Denver found that living near overhead distribution lines significantly increased the risk of certain kinds of childhood cancers. No measurements of electrical quantities were made. The hypothesis advanced as an explanation was that the magnetic field would be the causative agent and that the magnetic fields could be estimated by counting the number of conductors on the line and measuring the distance to the home, termed â€œwiring configurationsâ€. By estimating the induced current density in humans standing below the power lines, one learns that the electric field must be considered as a possible causative agent. The follow-on study in Denver failed to properly measure the fields directly under the power line. The defined wiring configuration codes failed to account for the spacing of the conductors or the location of the residence with respect to the supply substation. The idea that wiring configurations (a.k.a. wiring codes) estimate magnetic fields is erroneous. The studies in Denver, Los Angeles, Sweden, Finland, and a large area in the USA have found insufficient confidence in the magnetic field hypothesis, possibly because of many other physics errors; e.g., ignoring the role of vector direction, time and space averaging, not measuring any reasonable aspect of the power line electric fields and ignoring the engineering design differences in the transmission and distribution systems. The Scandinavian studies concentrated on 115 kV to 400 kV bulk transmission lines; yet, failed to consider the electric fields which induce at least ten times greater current density in a human than do the magnetic fields near the same lines. The cumulative effect of these serious errors in engineering physics is that the past decade of funded research has failed to explain why living adjacent to overhead distribution power lines in Denver and Los Angeles and living within 50 meters of bulk transmission lines in Sweden increases the risk of childhood leukemia
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Now as far as effecting value, it is like any other percieved short coming or speciality, it is in teh eyes of the Buyer. that's why we look to get that Listing in front of every possible person, so we can raise teh possibility of finding the "right" Buyer. Best of Luck! The Coach