The science, in detail
The World Health Organization's cancer agency (IARC) classifies power-frequency magnetic fields as possibly carcinogenic to humans (Group 2B). That rests on studies finding childhood leukemia about twice as common where children's average exposure is above 3–4 mG. Along this line, that level reaches roughly 200 ft from the centerline.
A cause-and-effect link has not been established, and the international exposure limit for the public is 2,000 mG. The haze uses typical published values for 500 kV lines (87 mG under the line, 29 at 50 ft, 12.6 at 100 ft, 3.2 at 200 ft, 1.4 at 300 ft). Actual fields depend on SDG&E's final design and on how much current the line carries, and are higher at peak load.
The comparisons with a home use about 1 mG, a common level inside homes. The zones are drawn at about 100 ft (12.6 mG), about 195 ft (3.5 mG, the middle of the 3–4 mG range in the leukemia studies) and about 355 ft (1 mG).
How accurate this is
Parcel lines are exact; the dots are not. The line comes from SDG&E's corridor-level maps, and SDG&E has not published an engineered alignment or tower sites. The dots here are spaced evenly at about 1,600 ft, the middle of the 1,400 to 1,800 ft span range reported for this project; real spans vary with terrain.
From the west end to about 5 mi past Lake Henshaw, the line is traced from the blue line on SDG&E’s South Mountain Alternative map. The map was placed by fitting its reservation areas (Pala, Pauma, Rincon, La Jolla, San Pasqual) to SANDAG boundary coordinates. With that fit, the county line, I-15 and Lake Henshaw on SDG&E’s map land on their real positions. The blue line as drawn is several hundred feet wide at the map’s scale, so the dots follow its center.
From there east to San Felipe Road, positions are good to about 600 ft. The west end is where SDG&E’s map stops; the line continues west out of frame.
Turn on the SDG&E maps layer and fade it to judge the fit yourself: their white roads should sit on the real roads.
Sources: magnetic-field values from Dominion Energy’s EMF brochure (typical 500 kV levels); IARC Monograph 80 and WHO Fact Sheet 322 on cancer classification; SDG&E corridor maps (South Mountain Alternative map and an earlier map photo), SANDAG reservation, county, road and lake boundaries, U.S. Census Bureau 1:500k AIANNH boundaries, SANDAG/SanGIS parcels, Esri and USGS base maps.