If the new lines were to be built next to the existing lines it would mean high vulnerability to any natural or manmade disaster. It should be recognized that these lines run unguarded for thousands of miles and serve the whole of the Northwest and California.
The loss of power for any prolonged period of time would be devastating from both monetary and human terms. Such a real life scenario was realized in the 1977 NY City blackout.
Separating of the lines on a new corridor would make such a simultaneous occurrence negligible. While one set of lines may be disabled, the other line could continue to fulfill the critical needs of the large US region.
BPA should not make this major decision based on the easiest way or least initial costs. Serious consider should be given to the best long term decision and the Total Cost of Ownership. Expenses are not just the upfront costs!
…why does BPA seem to be ignoring this major factor?

Thank you for an excellent and thorough job on this, David. This is very meaningful to our community.